Teacher’s Guide
1
1
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ISBN-13: 978-0-19-547141-0
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Contents
Introduction ............................................................................2
Chapter 1
Inheritance and selection .........................................................6
Chapter 2
Reactions of metals ...............................................................16
Chapter 3
Energy and electricity ............................................................25
Chapter 4
Fit and healthy ......................................................................38
Chapter 5
Patterns of reactivity..............................................................47
Chapter 6
Gravity and space ..................................................................57
Chapter 7
Plants and photosynthesis .....................................................65
Chapter 8
Environmental chemistry .......................................................74
Chapter 9
Speeding up ..........................................................................82
Chapter 10
Where does our food come from? ..........................................93
Chapter 11
Using chemistry ..................................................................101
Chapter 12
Pressure and moments ........................................................109
Sample lesson plan (Unit 2) .................................................121
Sample lesson plan (Unit 12) ...............................................122
Test paper 1 ........................................................................123
Test paper 2 ........................................................................127
Introduction
Teaching science effectively
Today we no longer question the importance of science in everyday life. Each of us knows that scientific
discoveries have drastically altered the dimensions of our lives, our world, and our universe.
To a scientist, trained with directed curiosity and a thirst for knowledge about the unknown, science means
much more than the products of discovery and invention. To him, science is a body of organized and tested
knowledge. It is also a way of thinking and working that is helpful in solving problems. Thus science has
both content and method.
Most educators agree that the purpose of education is to change the way in which people think, feel, and
act. In other words, education aims to modify behaviour. Every science teacher should therefore try to answer
this question: How can I teach science so that it will become a way of living, of reacting to the environment,
of interpreting the world in which we live? Science taught in this way is not just a collection of facts about
our world; it creates a behavioural pattern.
When we teach to bring about such changes in the behaviour of our students, we should test our results by
asking: Can the students think scientifically? Do they understand what science is all about and how scientists
go about their work? Do they have a positive feeling towards science and scientists? Are they likely to read
scientific books in later life with enjoyment and understanding?
Learning and teaching
Learning is most likely to occur when a student has a definite purpose. Science teaching should be focused
on the nature, methods, and aims of science. Science differs from other school subjects because it involves
a method of discovery based on experimentation. Experiments help to answer questions by observing the
effects of making systematic changes. New concepts must be based on an adequate background of firsthand experiences.
The task of the teacher is to set up a learning situation in which the student carries out activities focused
on understanding. The learning activities must also be adapted to the individual needs of the students. In
order to produce an active response from different students, different types of activities should be offered.
Making observations, performing experiments, planning ways to find out something, interpreting pictures
and diagrams, reading science content, etc. call for different types of thinking and skills. A variety of
activities help students to grasp concepts from different directions and therefore result in a greater depth
of understanding.
The teaching cycle
According to psychologists, learning focused on understanding must pass through a definite cycle. The
steps in learning may be termed:
1. Stimulus or raising questions and problems
Effective learning starts with a stimulus. To raise a question or problem, the situation must be meaningful
to the student; that is, it must be connected with his or her personal experience. The situation must also
be concrete and interesting enough to challenge him/her to find a solution.
2. Assimilation or achieving experience
This step is a search for the information needed to answer the question or solve the problem. Students
perform experiments, go on field trips, use visual aids, interview people, refer to books, etc. In short,
students use any source of information that will provide them with the facts needed to support their
enquiry.
Much of the information gathered by the student is specific because it has been derived from particular
experiences. However, these facts are useful only in identical situations. To be useful in other situations,
specific facts must be generalized.
3. Reaction or using the generalization
Practice in the application of the new understanding must now be provided. There should be many
situations in which the student can use the generalization to explain, predict, and plan.
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Organization of the book
The Science Fact file series provides a well-balanced and organized course in science, emphasizing the
acquisition of knowledge to be used as a guide for intelligent behaviour in daily life. It is not only a collection
of facts about the world around us. Instead, the content is focused on the acquisition of general concepts.
These general concepts are developed through several problem-solving methods.
To help the students develop thinking skills, appropriate study materials should be organized and concepts
developed so that they follow the patterns of effective thinking. Though the units are developed in various
ways, they all share the same general plan or structure. The pictures and text are designed to orient and
motivate the students. They help them understand the content of the unit and its importance. The layout has
been designed to arouse an active, inquiring interest in the unit.
Experiments and observations are introduced whenever the student may obtain information by direct
experience. At the end of each page there is a set of self-testing exercises. These test the student’s
comprehension of the concepts that have been presented.
About the Teacher’s Guide
Science Fact file Teacher’s Guide 1, 2, and 3 have been written to help the teacher develop effective science
teaching. The guide goes through each unit, giving suggestions for teaching procedures and supplying
answers for questions and solutions for exercises and problems.
Background information
This section will prove very helpful to teachers as it contains the scientific knowledge necessary to teach a
particular unit.
Unit introduction
Below are some of the ways in which a unit can be introduced. Most of them can also be used to start new
problems within the unit.
1. Ask questions about the students’ experiences in relation to the unit.
This method provides an inventory of past experiences and is thus, in effect a pretest. Ask the students
questions such as: Have you ever seen…? What did it look like? Have you ever made a…? Have you ever
heard about…? Have you ever watched someone…? The purpose of these questions is to obtain some
facts from the students’ past experiences.
Any questions that cannot be answered should be written on the board under the heading ‘Questions we
cannot answer’.
While questioning, the teacher should bear in mind that the purpose is not to get the correct answers.
It is to find out what the students know and how they think. Another purpose is to get the students to
ask their own questions. As the discussion progresses, the main points of the answers may be recorded
on the board. The students can then read the text to check their responses and also find answers to the
questions.
2. Using pictures
Pictures make it possible for the students to learn indirectly from other people’s experiences. Students
should be encouraged to study the pictures on the opening pages of a unit. To provide help to develop
the concept, several thought-provoking questions should be asked about the pictures.
3. Reading and discussion
Reading is a necessary and desirable activity for learning science, but too often it is the only activity.
This is probably because reading is the medium most familiar to teachers, who feel more at ease when
using it. Though science concepts are best developed through first-hand experience, sometimes, it is
impossible to provide experiments that are simple enough for secondary level students, or they require
laboratory facilities far beyond the resources of the average school. It is equally impossible to organize
actual observations of all living things in their natural habitats.
Though pictures can often substitute for direct experience, not everything can be illustrated. Therefore,
the text must provide factual information. The text has been planned to guide the student’s thinking
and help him organize his ideas. Thus reading is a means to an end and not an end in itself. The text
should not be thought of as a mere body of facts to be memorized by the student and then recited to
the teacher on demand.
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4. Experiments and observations
These can be experiments given in the book or provided by the teacher. The purpose is to explore
phenomena that require explanation. There are various ways in which the teacher may use the experiments
and observations depending on the time and the materials available, and the size of the class. Ideally
each student should do his own work; but this is not possible in many schools. Satisfactory results may
be obtained by having groups perform the experiments and make observations. However, the teacher
should make sure that each student has an opportunity to work within a group. If an activity takes several
days to prepare or carry out, the group should be selected in advance.
Before any experiment or observation is performed, ask questions such as: what is the purpose of this
experiment? What are we trying to find out? Why? This is effective as the teacher can discover from the
answers whether the students understand what is going to be done.
When the results have been observed and recorded, ask the students what was done in the experiment
and what happened. Do the results answer the questions posed at the start of the experiment? How do
they explain what happened?
The students should understand that it is highly unscientific to generalize from a single instance.
Explain to them that it may not be possible to do many additional experiments in the science class, but
reputable scientists insist upon performing many experiments before a general conclusion is reached and
accepted.
Whenever possible, students should obtain facts by first-hand observation. These facts will require
explanations. Ask students to collect and bring to class specimens of materials and living things. They
can then examine the specimens and look for the similarities and differences between them.
5. Field trips
Another means to provide opportunities for first-hand observation is through field studies. To decide
what to observe and what questions to ask, the teacher should first study the unit thoroughly, and then
take a walk to find out what first-hand information is available to help solve problems raised in the unit.
Make a list of the things that can be seen and the questions that can be asked. Then take the students
on the trip and have them make their observations. When they return to class, ask them questions that
bring out the facts obtained and call for explanation of these facts.
Teaching procedure
After the unit has been introduced, the students will have questions. The teacher should now develop the
concepts that can be understood before the students can answer the questions.
Different concepts require different methods of development. If the concept involves the characteristics of
a group of living things, materials, etc., various members of the group are described and the characteristics
common to all members pointed out. If a relationship concept needs to be developed, examples of the
relationship are discussed and a generalization about this relationship is made from the examples. If the
concept is a principle by which a device or process works, the development can be carried out in the following
steps:
i)
What does the device or process do or what is it used for?
ii) What are its parts and how are they arranged?
iii) How does the device or process work?
iv) A step-by-step explanation of what happens when it works.
In the Science Fact file series, the concepts are developed through the use of three important media:
i)
First-hand experiences such as experiments and observations because students learn most effectively
through ‘doing’ and being actively involved
ii) Visual aids such as pictures, diagrams, graphs, and charts
iii) Text or reading material.
Any or all of these media may be used to develop an individual concept.
When the study of the unit has been completed, the students should discuss the unit as a whole in order to
organize their ideas.
Answers
These provide, where possible, the expected results of any activity and answers to any questions present in
the units, including the Test yourself section. They also contain answers to questions in the workbook.
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Problems to solve and multiple choice questions
Additional questions have been provided for reinforcement purposes. A set of multiple choice questions is
also available at the end of each unit to check understanding of concepts. The teachers can also develop
their own multiple choice questions.
Projects and activities
A variety of projects and activities have been included in the Teacher’s Guide to meet the needs and interests
of different students in different localities. There are suggestions for planning and carrying out experiments
and observations, taking field trips, collecting specimens, assembling scrapbooks, building models, making
charts and drawings, and using reference books.
Lesson plans and test papers
Sample lesson plans and test papers have been provided at the end of the guide.
Finally a word about what we would like to achieve through this course. Our aim is to give students information
about themselves and the world they live in, upon which they can base opinions, derive judgements, and
determine courses of action in later life. We certainly do not see our suggestions as mandatory. We hope
they will supplement and support the teacher’s own professional practice. After all, no book can replace a
good teacher!
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5
C
1
er
hapt
Inheritance and
selection
Unit flow chart
Sex cells and fertilization
Patterns of inheritance
Selective breeding
Cloning
Aims and learning objectives
•
To introduce the role of chromosomes and genes in the inheritance of characteristics
•
To identify some inherited characteristics
•
To draw diagrams showing how sex cells are produced and fertilized
•
To describe how sexual reproduction results in genetic information being inherited from both parents
•
To understand terminology used in genetics
•
To show how selective breeding results in new varieties of animals and plants
•
To show how asexual reproduction results in the formation of clones
Background information
The people that you see in the pictures on page 2 belong to one type or species of animal. Scientists call
this species Homo sapiens. As you can see, the people have lots of things in common. For example, they
have the same general body shape and their faces have similar features. However, even though they are
easily recognizable as humans, there are lots of small differences between them. These variations are very
important and have helped Homo sapiens to evolve over millions of years into very successful animals.
Introduction to the unit
Ask the students: in what way do we resemble each other? In what way do we resemble our parents?
Explain that many of our features, for example hair colour, eye colour are controlled by a pair of genes.
These colours were determined at the time when the egg was fertilized by the sperm. The passing on of
characteristics from one generation to the next is called heredity. The study of heredity is called genetics.
While teaching this chapter, try to be as clinical as possible in your explanations.
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Teaching procedure
Ask the students: do plants reproduce? How?
Dissect a flower longitudinally and show the male and female parts of a flower with a magnifying glass.
Discuss the structure and formation of pollen and eggs in the anther and ovary of a flower. Explain that
in the same way some of the cells in your body are called sex cells or gametes. In a male body they are
called sperms and are made in the reproductive organs called testes. In the female body they are called
ova or eggs and are made in the ovaries.
Have the students comment briefly on the pictures on page 2.
Ask the students: how many chromosomes are there in body cells? In gametes?
Explain with the help of diagrams on the board the structure of chromosomes and explain the formation
of sex cells or gametes. Also explain that the number of chromosomes in sex cells is reduced to half.
Ask the students: why do you think that sex cells have half the number of chromosomes as compared to
body cells?
Explain that like pollination and fertilization in plants, sexual reproduction also occurs in animals and
human beings.
Ask the students: what is fertilization?
Explain that the union of the male and female sex cells is called fertilization. Sex cells are made by a kind
of cell division in which the number of chromosomes in the sex cells is reduced to half. At fertilization, a
male sex cell joins up with a female sex cell to make a fertilized egg cell called a zygote. The zygote has
the same number of chromosomes as those of the body cells of the species.
For example: In humans,
Number of chromosomes
in body cells
in male gametes
in female gametes
46
23
23
At the time of fertilization
sperm
23
+ egg
=
fertilized egg
body cells of baby
46
46
23
Ask the students: who do you resemble in the family?
Explain that we inherit characteristics from our parents through their chromosomes.
A chromosome has small parts called genes all the way along it.
Genes are made of a chemical called DNA. Genes control the development of inherited characteristics, such
as eye colour, hair colour, etc.
Ask the students: what happens to genes during fertilization?
Explain that a sperm has 23 chromosomes with genes from the father. An egg has 23 chromosomes with
genes from the mother. During fertilization the sperm and the ovum join together. Each chromosome from
the sperm then pairs up with a matching chromosome from the egg. This brings the two sets of genes
together.
For example, the genes for hair colour pair up and the genes for skin colour pair up and so on. It is
important to note that genes always work in pairs. Discuss the patterns of inheritance from the examples
given on page 5. Encourage the students to draw crosses of different characteristics of parents and try to
predict the results for the offspring.
The genes in a pair may be identical. For example, they may both produce black hair. But if one gene is
for black hair colour and the other for blonde hair, they are in competition.
Ask the students: how does the characteristic of one parent express itself in the offspring?
Explain that the gene that is able to express itself in the offspring is called a dominant gene. For example,
the black hair gene is dominant to the blonde hair gene as can be shown from the following example:
parents:
mother
father
characteristic:
black hair
blonde hair
genes:
BB
bb
gene alleles:
homozygous black
homozygous blonde
gametes:
B
b
zygote:
heterozygous black
Bb
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Ask the students: what kind of hair colour is present in the offspring? Where do you think the gene for
blonde has gone?
Explain that the gene for blonde hair colour is a recessive characteristic and it cannot express itself in the
presence of a dominant gene which in this case is the gene for black hair colour.
Ask the students: when do you think the blonde gene will be able to express itself?
Explain that the gene for blonde hair colour being recessive can only express itself if there is no dominant
gene around. That is there should be a recessive gene pair for blonde hair colour, only then will it be seen
in the offspring.
Write the gene pairs BB and bb on the board.
Ask the students: what do these represent?
Explain that the gene pair BB represents the gene for brown eye colour and bb represents blue eye colour.
Ask the students: if one parent has brown eyes and the other has blue eyes, what will the eye colour of the
baby be?
Explain that BB is the gene combination for a parent who has inherited B (brown eye colour gene) from
both parents. This type of genetic combination is called homozygous.
Ask the students: what do you think is the eye colour of bb?
Explain that it is blue.
Ask the students: if an egg carrying a gene for blue eyes is fertilized by a sperm carrying a gene for
brown eyes, will the person be homozygous or heterozygous for eye colour?
Write the genetic combination Bb on the board. Ask the students what it represents.
Explain that this type of genetic combination is called heterozygous. It represents one dominant and one
recessive gene. The physical appearance of the offspring will be brown eye colour as the dominant gene
will express itself. The recessive gene will be suppressed.
Now let us see what happens when both parents are heterozygous for hair colour.
parents:
mother
father
characteristic:
black hair
black hair
genes:
Bb
Bb
gene alleles:
heterozygous black
heterozygous black
gametes:
B and b
B and b
zygote:
BB
Bb
homozygous
heterozygous
homozygous
black
black
blonde
bb
Additional activity 1
A mouse has 40 chromosomes in each of its cells.
How many homologous pairs does it have? How many chromosomes are there in the sperm of a male
mouse?
Ask the students: how do you think varieties of different kinds of animals and plants are produced?
Discuss how Mendel discovered the behaviour of genes during crosses and their results. Explain that
Mendel, an Austrian monk, carried out simple experiments using garden peas. He noticed a number
of differences in their characteristics. For example, some plants were tall, some were dwarf, some had
smooth seeds, while others had wrinkled seeds.
During his experiments, Mendel carefully transferred pollen from the anther of a pure-breeding tall plant
onto the stigma of a pure-breeding dwarf-plant. He removed the anthers of the dwarf plant and covered
the dwarf plant with a bag.
Ask the students: why do you think he did this?
Explain that he did this to prevent pollen from different flowers pollinating the flower.
When the dwarf plant produced seeds, he planted them and observed the types of plants that grew. He
found that they were all tall.
Ask the students: what did his result prove?
Explain that it proved that the gene for tallness was dominant.
Next he planted the seeds obtained from the first experiment and allowed the plants to pollinate
themselves. When seeds were produced, he planted them and carefully recorded the results of his cross.
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What do you think was the result he got? Explain the result by drawing a Punnett square and explain the
results of Mendel’s experiment.
Additional activity 2
A pea plant has 14 pairs of chromosomes in each of its cells.
How many chromosomes will there be in a pollen grain cell?
How many chromosomes will there be in an egg?
How many chromosomes will be found in a pea plant grown from a seed?
Ask the students: a person with brown hair has dyed it red. What is the colour due to? Are there any
genetic changes?
Discuss that physical changes are not inherited. Only characteristics and changes in the genes can be
inherited.
Selective breeding
Show the students pictures of the two kinds of dogs in the pictures on page 6.
Ask the students: what features are common to both? In what ways are they different? Do dogs resemble
any other animal that you have seen?
Explain that all dogs belong to the same species and have a common ancestor, the wolf. In the same way
plants have also been selectively bred to produce crops, fruits, and vegetables.
Since civilization began, thousands of years ago, humans have been selectively breeding domesticated
animals and plant crops. New varieties of plants and animals are produced by deliberately selecting those
individuals who have the desired characteristics and breeding from them.
What effect will inbreeding have on the organisms that are produced by this method? Does it have
anything to do with genes?
Discuss the danger of inbreeding. Explain that continued breeding of closely related individuals is
common, especially in the production of ‘show’ animals like cats and dogs. Unfortunately this can lead to
infertility and reduced resistance to disease.
Additional activity 3
Carefully cut a piece of stem about 10 cm long from a geranium plant, money plant or other house
plant. Remove the bottom leaves leaving three or four at the top. Place your cutting in a jar so that the
bottom 4 cm is in water. Leave it until you can see roots growing from the stem. Once the new roots
are about 2 cm long you can plant your cutting in some moist compost.
What kind of a plant grows from the cutting? Is it like its parent plant? How many parents were involved in
making this new plant?
Asexual reproduction in animals
Do all organisms reproduce sexually? Explain that some organisms can reproduce asexually as well. This
type of reproduction needs only one parent.
Ask the students: what type of offspring will be produced? Whom will they resemble genetically? Will
they resemble each other? What are these offspring called? What are the advantages of this type of
reproduction? What are its disadvantages?
Clones
Ask the students: what is a clone? Have you heard of Dolly, the cloned sheep? Discuss how Dolly was
cloned and what its characteristics were.
Discuss the disadvantages of cloning. Cloning reduces the size of the gene pool. This means that there are
fewer genes in the population.
Ask the students: what effect will this have on the clones? What is genetic variation? Why do you think
cloned organisms can become sick or even die if one plant or animal has a disease?
Discuss.
Answers
Inheritance and selection: p 2
1.
All living things inherit their characteristics from their parents.
2.
a)
Chromosomes are fine threads of materials which carry bits of information about what we look
like and how we behave.
S CIENCE F ACT
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T EACHER ’ S G UIDE 3
9
b)
Bits of information which are located on chromosomes are called genes.
3.
Genes are made of a chemical called DNA.
4.
Homologous chromosomes are pairs of chromosomes which carry information about the same
characteristic.
5.
a)
46
b)
23 pairs
Sex cells and fertilization: p 3
1.
A sex cell is called a gamete.
2.
a)
Male sex cells are called sperms.
b)
Female sex cells are called eggs.
3.
Four
4.
The male and female gametes carry 23 chromosomes each. After fertilization, the nucleus of the sperm
joins up with the nucleus of the egg. Each chromosome from the sperm pairs up with its partner from
the egg, making 23 homologous pairs altogether.
5.
As a new baby grows, more cells must be made. This happens by a process of cell division. Each new
cell has its own set of chromosomes carrying exactly the same information as the original fertilized
cell.
Patterns of inheritance (1): gene alleles: p 4
1.
a)
An allele is a different form of the gene for the same characteristic.
b)
A person may have two alleles (one pair) for hair colour: one for blonde hair and the other for
brown hair. These alleles are in competition with each other.
2.
A dominant gene allele is more powerful than the recessive gene allele in a pair of gene alleles. The
dominant gene is able to express itself in the individual whereas the effect of the recessive gene is
suppressed. For example, black hair colour is dominant to blonde. Brown eye colour is dominant to
blue.
3.
A person who has two identical gene alleles for a characteristic is homozygous for that
characteristic.
A person who has two different gene alleles—one dominant and one recessive—is heterozygous for
that characteristic.
4.
Hybrid means that an individual has one dominant and one recessive gene in an allele pair for a
particular characteristic.
5.
The person will be heterozygous for eye colour.
6.
A person with black hair could have a homologous gene pair for black hair, or he could have a
heterozygous gene pair for black hair colour, in which he could be carrying a dominant gene for black
hair and a recessive gene for blonde hair.
Patterns of inheritance (2): genetic diagrams: page 5
1.
Alleles are shown on genetic diagrams as letters of the alphabet.
2.
a)
Capital letters are used for dominant genes.
b)
Small letters are used for recessive genes.
3.
a)
brown
4.
a)
a and c b) b
5.
a)
b) brown
c) blue
Woman
blue eyes
Man
brown eyes
Alleles
b)
10
�
�
�
�
�
�
��
��
�
��
��
�
brown and blue
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Selective breeding (1): animals: p 6
1.
Selective breeding is also called artificial selection because humans artificially select only the most
productive animals and plants to breed from.
2.
Selective breeding works in this way:
•
Choose the animals and plants that have the best characteristics.
•
Breed them with each other.
•
Choose the best offspring and breed them with each other.
•
Repeat this over and over again to improve the characteristics.
3.
By choosing the cows which had the best characteristics and breeding them with each other. Then
choosing the best offspring and breeding them with each other. This process was repeated over and
over again to improve the characteristics.
4.
Ex-champion race horses have most of the dominant characteristics which a race horse should have.
When they are retired from racing, their sperm can be used to fertilize female horses to produce
hybrids which have good dominant genes for racing horses.
Selective breeding (2): plants: p 7
1.
Brussels sprouts, broccoli, cabbage, cauliflower
2.
a)
for many small side buds
b)
for large flower head
c)
for a swollen stem
3.
Selective breeding in plants is sometimes called selective pollination because the plant breeder selects
the pollen used in the crosses.
4.
To protect them from unwanted pollen from other plants.
5.
To prevent self-pollination.
6.
Asexual reproduction is used to make more copies of the same type of vegetable to retain the desired
characteristics which would otherwise be lost if the plants were allowed to cross-pollinate.
Cloning: p 8
1.
Clones are genetically identical organisms.
2.
Asexual reproduction is a kind of reproduction in which no gametes are involved. The new offspring
are exact genetic copies of the parent. Sexual reproduction takes place with the help of gametes.
3.
a)
identical twins
b)
Dolly, a white-faced lamb.
4.
In 1997, scientists at the Roslin Institute in Edinburgh, England, cloned a sheep called Dolly. They
removed the nucleus from an egg of a black-faced sheep. An egg was taken from a white-faced sheep,
and electricity was used to fuse the empty egg and the egg cell together. The new cell was put into
the womb of the black-faced sheep where it grew and Dolly, a white-faced lamb (clone) was born.
5.
Cloning reduces the size of the gene pool; there are fewer different genes in the population. Also
cloning does not give genetic variation, so if one plant or animal has a disease, it is likely that all the
other clones will catch it as well.
Test yourself: p 9
1.
2.
a)
i)
Chromosomes are fine thread-like structures which carry bits of information about what we
look like and the way we behave.
ii)
They are found in the nucleus of the cells of living organisms.
b)
Chromosomes are made of DNA.
c)
Each cell has its own set of chromosomes carrying exactly the same information as the original
fertilized cell.
a)
Gametes are sex cells.
b)
Sperms are made in the testes.
c)
23
d)
i)
Female gametes are called eggs.
ii)
They contain half the number of chromosomes as are found in the body cells or 23.
e)
When a sperm joins up with an egg the process is called fertilization.
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11
3.
a)
��
man
�
�
�
��
��
�
��
��
��
woman
b)
The allele for brown eyes is dominant.
c)
recessive
d) i) BB and bb
ii) Bb
e) i) BB and Bb
ii) bb
f)
4.
5.
A brown-eyed person may be homozygous or heterozygous for brown eye-colour.
a) i) Its long, sleek body
ii) its strong limbs
b)
Thick fur
c)
New varieties of dogs are produced by deliberately selecting those individuals that have desired
characteristics and breeding from them. For example, to produce a hunting-dog breed the
characteristics such as sharp teeth, long thin legs, and a good sense of smell can be selected
from a breed that has these characteristics.
d)
The characteristics of both breeds are very different. So in order to get the desired characteristics
it would take several crosses. It would also take a very long time for the individual to grow up
and show the characteristics that it has acquired.
a)
Clones are genetically identical organisms.
b)
Asexual reproduction
c)
Production of kale from wild mustard.
d)
Cuttings are used to make copies of the ‘new’ plants. If the plants were allowed to cross-pollinate,
genes from different varieties would be involved in the process of sexual reproduction and new
combinations would be made. In this way the desired characteristics would soon be lost.
Workbook 3, chapter 1
1.
2.
a)
i)
It is an animal cell.
ii)
It has no definite shape. It has a nucleus in the centre. It has a thin cell membrane.
b)
In the nucleus.
c)
DNA
d)
Gene, chromosome, nucleus, cell
a)
i)
2 pairs
b)
i)
Gamete
ii)
It has chromosomes in pairs, gametes or sex cells have single chromosomes only.
c)
ii)
homologous chromosomes
i)
reproductive cell in ovary or testis
homologous
chromosome pairs separate
replication of chromosomes
sperms or eggs
12
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egg
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T EACHER ’ S G UIDE 3
sperm
sperms or eggs
ii)
egg
sperm
fertilized egg
replication of chromosomes
new cells formed
further replication of chromosomes
more new cells
3.
a)
tall pea plant
pollen
Tt
T
t
T
tall pea plant
TT
Tt
Tt
tt
Tt
t
eggs
4.
b)
T
c)
t
d)
i) TT, tt
ii) Tt
e)
i) TT, Tt
ii) tt
a)
Usually a fine paint brush is used to transfer pollen from one plant to another.
b)
The pollinated flower is protected from unwanted pollen.
c)
The plant breeder selects the pollen used in the crosses.
d)
i)
It is sexual reproduction.
ii)
The pollen is transferred from the anther of one flower to the stigma of another flower.
5.
Selective breeding is also called artificial selection and involves sexual reproduction. Scientists use it
to produce new varieties of animals and plants. It has been used to produce farm animals and crop
plants with greater yield and resistance to disease. Selective breeding takes several generations.
6.
a)
The cart horse has to pull heavy loads so it has short, thick legs, broad hoofs, a sturdy body,
and a strong neck.
The race horse has long, thin legs, narrow hoofs, a sleek body and a long thin neck.
b)
7.
Horses that have the desired characteristics are chosen and bred with each other. The best
offspring are chosen and bred with each other. This is repeated over and over again to improve
the characteristics.
sexual reproduction
asexual reproduction
Male and female sex cells join together
No joining of sex cells
Offspring are not genetically identical
Offspring genetically identical
Two parents are needed
Only one parent needed
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Problems to solve
1.
E is the gene for brown eye colour and e is the gene for blue eye colour. Which gene is dominant?
2.
Both father and mother have the genes Ee in their cells. What colour are their eyes?
3.
Copy the diagram below. Complete it to show how the genes in each sex cell come together at
fertilization.
mother
E
mother
e
E
E
e
E
father
father
e
E
4.
Which of the fertilized cells are homozygous for eye colour? Which are heterozygous?
5.
Which zygotes will produce children with blue eyes? Which will produce children with brown eyes?
Solutions to problems
1.
Brown eye colour (E gene) is dominant.
2.
Brown eyes because E is a dominant gene and they both have it.
3.
mother
E
mother
E
e
EE
Ee
father
E
e
E
EE
Ee
E
EE
Ee
father
e
Ee
ee
4.
Those that carry the genetic combination EE or ee are homozygous. Ee are heterozygous.
5.
Those that have the genetic combination ee will be blue-eyed. Those with the genetic combination Ee
will be brown-eyed.
Multiple Choice Questions
1.
Living things inherit their characteristics from their
A brothers
2.
B sisters
A AND
3.
B NDA
Human cells have
A 23
4.
7.
B eggs
D NAD
C 32
D 40
C testes
D ovaries
A person who has two identical gene alleles for a characteristic is called
B dominant
C heterozygous
D homozygous
Genetically identical organisms are produced by
A asexual reproduction
B sexual reproduction
C genetic variation
D selective breeding
If ‘H’ represents a gene for black hair and ‘h’ an allele for blonde hair, what would be the genetic
combination of their offspring having blonde hair?
A HH
14
C DNA
Male sex cells are called
A recessive
6.
D friends
chromosomes
B 46
A sperms
5.
C parents
Chromosomes and genes are made of a chemical called
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T EACHER ’ S G UIDE 3
D hH
8.
During selective pollination in plants, self pollination is prevented by removing the
A stigma
9.
B stamens
C ovules
D pollen
Modifying the information carried by an organism by inserting a different gene produces a
A GMO
B MGO
C OGM
D MOG
10. Whenever a dominant allele pairs up with a recessive allele, the final effect is produced by the
A recessive gene
B dominant gene
C both genes
D opposite genes
Answers
1.
C
6. A
2. C
3. B
4. A
5. D
7.
8. B
9. A
10. B
C
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2
Reactions of metals
er
C
hapt
Unit flow chart
Properties of metals
Metals and acids
Acids and metal carbonates
Acids and metal oxides
Titration
Some common salts and their uses
Aims and learning objectives
•
To show the properties of metals
•
To use the particle model to explain the properties of metals
•
To learn how different acids react in a similar way with metals, metal carbonates, and metal oxides
•
To identify patterns in these reactions and produce general equations
•
To use word and symbol equations to describe chemical reactions
•
To name some salts and describe some uses for them
Background information
We use a large variety of metals every day. Many of them are relatively new materials, such as plastics
and composite materials. Some of the most important ‘old’ materials in use today are metals. During the
16
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Bronze Age, people found that if they heated rock containing copper with carbon, they produced copper.
This was then mixed with tin to make an alloy called ‘bronze’. Bronze was very hard and was used to
make tools.
A more reactive metal, iron, was obtained in a similar way. The properties of iron made it a much more
useful metal than copper. However, it was not until the early 19th century that today’s most important
metals were discovered. In general, the more difficult it is to extract a metal, the later it was discovered.
We get some metals from the sea, but most from the Earth’s crust. Six main metals are found in the
Earth’s crust. Aluminium is the most abundant of these, and iron is next. None of the six is found
uncombined, because they are all reactive metals, and reactive metals ‘like’ to form compounds. Some
metals such as copper, mercury, zinc, silver, lead, gold, tin, and platinum are a few of the scarce metals.
The rocks in the Earth’s crust are a mixture of many different compounds. But some contain a larger
amount of just one metal compound, or one metal and it may be worth digging these up to extract the
metal. Rocks from which metals are obtained are called ores.
Unit introduction
Ask the students: what is a metal? What are metals made of? What are the properties of metals?
Explain that metals are crystalline materials. If you look at something made of galvanized iron such as a
dustbin or a new lamp post, you may be able to see zinc crystals. These crystals are irregular in shape.
Extracting metals from minerals
Additional activity 1
Put some crushed galena (compound of lead sulphide) into a soft drink bottle cap. Remove the plastic
disc inside first. Strongly heat the sample with a Bunsen flame for 10 to 15 minutes. Test the gas given
out with a wet pH paper.
What does the colour of the wet paper become? (pink/blue)
Is the gas given out acidic or alkaline?
Look at the solid left. Do you think that a metal has been formed?
Explain that to obtain the metal lead, sulphur must be removed.
Growing lead crystals
Additional activity 2
Put a strip of zinc metal into a solution of lead nitrate. You will notice that after a short time lead
crystals are formed.
Why do you think this happens?
[Hint: think about the reactivity series]
Teaching procedure
Ask the students: what are metals made of?
Explain that by looking at metals with X-rays, it can be seen that the atoms in a metal are held closely
together in a regular pattern.
Understanding the properties of metals
Additional activity 3
You will need pieces of copper, zinc, lead, and iron.
Polish the surface of each metal with a piece of sand paper. Look at the surface carefully.
What do you see?
Connect the metals to a simple circuit with a bulb.
Does the light bulb glow each time?
The general physical properties of metals are:
•
High densities
•
High melting and boiling points
•
Good conductors of heat and electricity
•
Malleable and ductile
The properties of a particular metal depend on the way the atoms are arranged in the crystal, and on the
crystal size.
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The average density of metals is about 8g/cm3. This is much higher than non-metals. One factor which
affects the density of an element is the way in which the atoms are packed together.
Metal
Density(g/cm3)
Copper
8.9
Gold
19.3
Iron
7.9
Magnesium
1.74
Nickel
8.9
Potassium
0.86
Sodium
0.97
Ask the students: can you boil a metal?
Explain that the bonds between metal ions are so strong that it takes a lot of energy to melt or boil a
metal. The outer electrons in a metal atom are able to move freely through the metal as a whole. We can
think of the electrons as forming a ‘sea’ of electrons around the much larger positive ions. Study the
movement of electrons using the diagram on page 11. Explain that the ‘sea’ of moving electrons in a
metal enables the metals to conduct electricity.
Metals can be hammered into different shapes and can be pulled into wires. When a force is applied to a
metal by pulling or hammering, the layers of atoms slip over each other.
Groups of crystalline areas are called ‘grains’. By making the grain size smaller, through heating and
cooling the metal, for different lengths of time, it is possible to make the metal stronger, harder, or more
brittle. In this way properties of metals can be adapted for particular jobs.
Reactions of metals
Ask the students: why do we need to know the behaviour of metals with certain compounds?
Explain that knowing about the chemical reactions of metals is vital when working out how to use them.
For example, knowing how a metal reacts with dilute acids can help us decide what metal to make a can
out of. The can may be used to store fruit, which contains natural, weak acids. How easily a metal is
attacked by oxygen in the air tells us how quickly a metal will corrode.
Reaction of metals with acids
Write the following equation on the board:
acid + metal ‡ metal salt + hydrogen gas
Explain that when a metal reacts with a dilute acid, hydrogen gas is given off and a salt is formed.
Magnesium reacts very quickly with the acids found in the school laboratory.
magnesium + hydrochloric acid ‡ magnesium chloride + hydrogen
Ask the students: do all metals react very quickly with acids?
Explain that not all acids react with acids. Sometimes metals react very slowly with weak acids, over many
years. Acid rain attacks some metals quite severely.
Acids and metal carbonates
Write the following equation on the board:
acid + metal carbonate ‡ metal + carbon dioxide + water
Explain that all metal carbonates react with dilute acids giving off carbon dioxide gas. During the reaction
fizzing or effervescence is usually seen and heard.
calcium carbonate + hydrochloric acid ‡ calcium chloride + water + carbon dioxide
Carbon dioxide does not burn. Fire extinguishers use the reaction of an acid with a carbonate to produce
carbon dioxide foam.
Acids and metal oxides
Many metal oxides are insoluble in water. But some can dissolve in warm water forming an alkali. Metal
oxides and hydroxide both react with acids to form salt and water.
Write the following equation on the board:
sodium hydroxide + hydrochloric acid ‡ sodium chloride + water
The salt formed by the reaction of sodium hydroxide with dilute hydrochloric acid is often called table salt.
Its correct chemical name is sodium chloride.
18
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Additional activity 4
Fill in the blanks to complete the table.
Method of preparation
Reactants
Salt formed
Other products
acid + carbonate
acid + metal
acid + alkali
acid + metal oxide
acid + base
Titration
Ask the students: how can we find out the concentration of solutions?
Explain that titrations are carried out in analytical laboratories to find the concentrations of solutions.
Explain the method of making a titration using an acid and an alkali. Make a practical demonstration.
Ask the students: why do we need to use an indicator during a titration? What is end-point? What are the
end products of a titration?
Explain the reaction by writing the chemical equation of a titration on the board. When a metal such as
magnesium reacts with a dilute acid, the hydrogen in the acid is replaced by the metal. When the reaction
is complete the acid is said to have been neutralized. Metal carbonates also neutralize acids. When an acid
is neutralized, salt and water are formed, and during the reaction the pH of the acid changes. The reaction
is complete and the acid neutralized when the pH of the solution reaches 7. The salt formed during the
reaction depends upon which acid and which metal is used.
Different acids make different salts
Ask the students: how can we tell what salt will be formed by a chemical reaction?
Explain that the type of salt depends on the type of acid used. For example:
Name of acid
Chemical formula
Name of salt
ethanoic (acetic)
CH3COOH
ethanoate (acetate)
hydrochloric
HCl
chloride
nitric
HNO3
nitrate
sulphuric
H2SO4
sulphate
phosphoric
H3PO4
phosphate
Common salt and its uses
Ask the students: where is common salt found? How is salt important in our daily lives?
Explain that salt is found underground as rock salt. Rock salt is put on icy roads in winter because it
lowers the freezing point of water to below 0°C.
Salt water speeds up corrosion and rusting. The correct amount of salt is very important in our diets. Too
little salt can cause circulation problems. However, too much salt can cause high blood pressure and heart
disease.
Before the days of refrigeration, salt was used to preserve food.
Salt is the main raw material for making chlorine and sodium hydroxide. A concentrated salt solution,
called brine, is electrolysed.
Explain the electrolysis of sodium chloride solution with the help of diagrams on the board.
Ask the students: where else do we find common salt?
Explain that sea water contains a lot of salt.
Salts found in sea water
Explain with the help of a chart the kinds of salts present in sea water.
The sea contains about 25g of sodium chloride per litre of sea water. It also contains many other salts:
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Salt
Amount in g/100g of sea water
Sodium chloride
2.6
Magnesium chloride
0.3
Calcium sulphate
0.2
Potassium chloride
0.1
Magnesium bromide
0.01
Magnesium iodide
0.0003
Salts as fertilizers
Ask the students: besides food, what are salts used for?
Discuss the uses of salts as fertilizers. Explain that a good fertilizer contains the elements needed to
promote healthy growth in plants.
Ask the students: what are the most important elements in fertilizers?
Discuss the list of useful salts on page 17 of the student’s book.
Answers
Reactions of metals: p 10
1.
a)
Properties of metals:
they can reflect light
they are malleable and ductile
they can conduct heat and electricity
they have high melting points
b)
Jewellery is made of gold.
Car bodies are made of steel.
Electricity cables are made of copper.
Cooking pots are made of aluminium.
2.
a) graphite
3.
Metals are used for making laboratory apparatus.
4.
b) diamond
c) plastic
metals
uses
aluminium
wall facings, aeroplanes, engines, roofing, ships, windows, and doors
copper
wires
gold and silver
jewellery
steel
bridges, car bodies, cutlery, hammers, sheets, tools, and wires
Metals are malleable and they do not break easily. So they can prevent injury to the passengers.
Understanding the properties of metals: p 11
1.
The arrangement of the atoms in metals makes them behave in the way that they do.
2.
The high density of metals is because the atoms are very closely together.
3.
a)
4.
5.
20
i)
Malleable means can be hammered into shape.
ii)
Ductile means can be drawn into wires.
b)
Metals can be hammered into shapes because the layers of atoms can slip over one another by
the pushing and pulling forces applied on them.
a)
Electrons are arranged such that they form a sea around the much larger positive ions. As a result
they are able to move freely through the metal as a whole.
b)
When an electrical voltage is connected to the meal, an electric current flows because the electrons
are free to move.
Non-metals do not have a sea of electrons in their structure so they do not conduct electricity.
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Metals and acids: p 12
1.
Many metals are more reactive than hydrogen gas.
2.
Hydrogen gas is given off.
3.
When a metal is added to an acid, the hydrogen of the acid is displaced and a new chemical compound
is formed. This compound is called a salt.
4.
Add some zinc metal to sulphuric acid in a beaker. Hydrogen gas bubbles off. When the bubbles stop
forming, the acid has been neutralized. Filter the solution to remove any unreacted zinc. Carefully
heat the filtrate to evaporate the water. A white compound is left behind. This is zinc sulphate.
5.
zinc + sulphuric acid ‡ zinc sulphate + hydrogen
Zn + H2SO4 ‡ ZnSO4 + H2
Acids and metal carbonates: p 13
1.
a metal salt, carbon dioxide, and water
2.
Add enough amount of lead carbonate to nitric acid in a beaker. Carbon dioxide bubbles will be
given off. Remove any unreacted lead carbonate by filtering the solution. Heat the filtrate carefully to
evaporate the water. The white compound left behind is lead nitrate.
3.
lead carbonate + nitric acid ‡ lead nitrate + carbon dioxide + water
PbCO3 + 2HNO3 ‡ Pb(NO3)2 + CO2 + H2O
4.
a)
calcium carbonate + sulphuric acid ‡ calcium sulphate + water + carbon dioxide
b)
The reaction soon stops because the salt, calcium sulphate, which is formed, is insoluble and
forms a film around the marble chips (calcium carbonate) preventing more acid reacting with the
marble.
Acids and metal oxides: p 14
1.
Any substance that can neutralize an acid is called a base.
2.
A base that is soluble in water is called an alkali.
3.
Metal oxides dissolve in acids.
4.
Add copper(II)oxide to sulphuric acid and heat them until warmed. Copper(II)oxide dissolves and the
solution turns blue. Add more copper(II)oxide until no more of it dissolves. Remove the undissolved
copper oxide by filtration. Heat the filtrate carefully to evaporate some of the water. Leave it to cool.
Blue crystals of copper sulphate are formed.
5.
copper(II)oxide + sulphuric acid ‡ copper(II)sulphate + water
CuO + H2SO4 ‡ CuSO4
+ H2O
Titration: p 15–16
1.
A titration is an experiment to find out how much alkali is exactly needed to neutralize an acid.
2.
The point at which an alkali just neutralizes an acid is called the end point.
3.
greenish-yellow
4.
26cm3
5.
Red litmus would have turned red at the end point, while blue litmus would have turned blue indicating
that a neutral point has been reached.
6.
The acid is added drop by drop very carefully.
Some common salts and their uses: p 17
1.
sodium chloride
2.
Electrolysis is used to obtain useful substances from sodium chloride.
3.
chlorine, hydrogen, and sodium hydroxide
4.
Fertilizers contain elements such as nitrogen that plants need to keep them healthy.
5.
In industry, ammonium nitrate is made by reacting ammonia with nitric acid. For this reason, the
manufacture of ammonia and nitric acid is carried out close to each other to reduce costs.
6.
nitrogen
Test yourself: p 18–19
1.
b, d, f, h, j
2.
a)
It is a displacement reaction; hydrogen is replaced by zinc.
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21
b)
3.
4.
5.
i)
hydrogen
ii)
Bring a burning match near the gas. If the gas is hydrogen, it burns with a blue flame and
makes a popping sound.
c)
zinc + hydrochloric acid ‡ zinc chloride + hydrogen
d)
The reaction would be faster.
a)
magnesium sulphate
b)
ammonium chloride
c)
zinc nitrate
d)
copper sulphate
e)
silver chloride
f)
copper nitrate
a)
Magnesium oxide dissolves in it.
b)
So that all the acid is used up.
c)
By filtration.
d)
The filtrate is heated carefully to evaporate some of the water. Then it is left to cool. Crystals of
magnesium sulphate will be formed.
a)
The pH changes from 1 to 7.
b)
water
c)
20cm3
d)
13
12
11
10
9
8
7
6
5
pH
4
3
pH value decreases
as acidity increases
2
1
0
10
20
30
40
Volume of sodium hydroxide
6.
7.
a)
It is found in the sea as well as rock salt.
b)
sodium hydroxide and chlorine
c)
This is done to dissolve the salt and bring it to the surface.
d)
It is so salty that nothing can live in it.
e)
Take a known quantity of sea water in a beaker and evaporate it to dryness by heating. Collect
and weigh the amount of salt that is left behind.
a)
Fertilizers contain nitrates which are very useful for plant growth.
b)
ammonium nitrate, calcium nitrate, sodium nitrate
c)
ammonium phosphate, potassium sulphate
Workbook 3, chapter 2
1.
22
Metals
Non-metals
high melting points
low melting points
malleable
many are gases
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2.
ductile
have low densities
good conductors of heat
poor conductors of heat
good conductors of electricity
poor conductors of electricity
shiny
make a noise when hit
a)
i)
The particles are closely packed.
ii)
Pushing or pulling forces make the layers in the crystal slip over one another. The metal does
not break but it does change shape.
iii) Metals have a sea of electrons which carry heat as they move. So copper is a good conductor
of heat.
3.
4.
5.
b)
When atoms in a metal are close together, their outer electrons are able to move freely through
the metal as a whole. When an electrical voltage is connected to the metal, an electric current
flows because the electrons are free to move.
a)
aluminium chloride + hydrogen gas
b)
tin sulphate + hydrogen gas
c)
lead nitrate + hydrogen gas
d)
copper nitrate + hydrogen gas
e)
iron sulphate + hydrogen gas
f)
magnesium chloride + hydrogen gas
a)
i) 4
b)
calcium carbonate + sulphuric acid ‡ calcium sulphate + carbon dioxide + water
c)
CaCO3 + H2SO4 ‡ CaSO4 + CO2 + H2O
d)
carbon dioxide gas
a)
Copper oxide dissolves easily in warm sulphuric acid. It reacts with sulphuric acid to form copper
sulphate which is blue in colour and so turns the solution blue.
b)
To use up all the acid.
c)
By filtering the solution.
d)
The filtrate is heated carefully to evaporate some of the water. It is then left to cool. Blue crystals
of copper sulphate begin to form.
e)
An alkali.
ii) 3
6.
A salt is made whenever an acid reacts with an alkali. It is possible to find out just how much
acid is needed to neutralize an alkali by carrying out a titration. This is an experiment that uses
equipment that can measure the volume of a solution accurately. Acid is added until a neutral point
is reached. The solution now contains salt and water. The salt can be obtained by evaporating the
water away.
7.
a)
For proper growth.
b)
i) bone meal, fish meal
c)
phosphate potash
d
i) no
ii) nitrate of potash
ii) All kinds of vegetables need phosphorus and nitrogen for healthy growth.
Project
Perform a chemical reaction that releases the gas carbon dioxide.
You will need: vinegar, baking soda, a balloon, a spoon, a narrow-necked bottle
Take a small narrow-necked bottle, and carefully pour in vinegar until it is about a quarter full. (Warming
the vinegar will speed up the reaction). Pour baking soda into the neck of the balloon through a funnel.
Fill the ball of the balloon with the soda. While keeping the balloon hanging down, stretch the neck over
the bottle neck. Once it is secure, lift the balloon quickly so that the soda falls into the bottle. Shake it if
necessary.
As soon as the soda meets the vinegar, it begins to fizz as carbon dioxide is released, slowly inflating the
balloon.
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Multiple Choice Questions
1.
Which one of the following is a non-metal which conducts electricity?
A copper
2.
3.
B gold
5.
B can conduct electricity
C can be drawn into wires
D are brittle
Metals react with dilute acids to produce
B carbon dioxide
7.
8.
D oxygen
A salt and water only
B salt and hydrogen only
C salt, carbon dioxide, and water
D salt, hydrogen, and water
A base that is soluble in water is called
B an alkali
C an oxide
D a metal
The reaction between copper(II)oxide and sulphuric acid will produce
A copper sulphate
B copper hydroxide
C copper oxalate
D copper chloride
When an acid and an alkali react together
A salt and hydrogen are formed
B salt and water are formed
C salt and oxygen are formed
D salt and an acid are formed
The colour of universal indicator in a strong acid is
A purple
9.
C hydrogen
Metal carbonates react with dilute acids to produce
A an acid
6.
D plastic
A have high melting points
A water
4.
C graphite
Which one of the following is not a property of metals?
B blue
C green
A good fertilizer contains
A hydrogen
D red
that plants need for healthy growth
B nitrogen
C oxygen
D carbon
10. Which one of the following is not a product of the electrolysis of common salt?
A chlorine
B hydrogen
C sodium hydroxide
Answers
1.
C
6. A
24
2. D
3. C
4. C
5. B
7.
8. D
9. B
10. D
B
S CIENCE F ACT
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T EACHER ’ S G UIDE 3
D oxygen
C
3
er
hapt
Energy and
electricity
Unit flow chart
Energy arrows
Power supplies and voltage
Resistance
Controlling the current
Safety and electricity
Paying for electricity
Energy for everyday use
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Aims and learning objectives
• To show the range of useful energy transfers
• To introduce the concepts of voltage and resistance
• To understand that all materials show resistance against the flow of electricity through them and that a
resistor can be used to control the current in a circuit
• To understand that current flowing through a resistance wire causes a heating effect
• To understand the difference between direct and alternating current
• To explain the importance of fuses and circuit breakers in mains electricity circuit
• To show that electric appliances transfer energy
• To recognize that electricity must be paid for
• To describe how electricity is generated with reference to environmental impacts
Background information
In our modern society we depend on electrical devices to do work for us. On p134 we can see some of the
electrical appliances which we use in our homes. Each one converts electrical energy into another form.
Energy is always lost in some form or another, usually in the form of heat.
All materials contain atoms. Atoms in turn contain small, electrically charged particles called electrons and
ions.
Unit introduction
Draw a Sankey diagram on the board. Ask the students: what does the diagram represent?
Explain that a simple way of showing what energy changes take place and where the energy goes is by
drawing a Sankey diagram, which looks like a set of arrows.
Ask the students: what is an electric circuit? Can it be represented by a Sankey diagram?
Draw a Sankey diagram of an electric circuit on the board and explain that an electrical circuit is a pathway
which charged particles can move along. The circuit diagram on page 21 of the student’s book shows a
circuit for operating various electrical appliances connected in a series. There is a complete path from the
positive end of the battery through the appliances and back to the negative end of the battery.
Teaching procedure
Set up a small circuit containing a bulb, a switch, and an ammeter. Switch it on. What happens? Explain
that in a circuit containing a light bulb we can judge the size of the current by looking at the brightness
of the bulb. A large current makes the bulb glow brightly. A small current makes the bulb glow dimly, or
not at all. This method is not accurate enough for scientific work, so a meter called an ammeter is used to
measure the current. When an ammeter is connected in a circuit, it measures the current flowing through
it.
Voltage
Show the students some dry battery cells. Help them to read the voltage marked on them. Set up a small
circuit carrying a voltmeter, a bulb, and a switch as shown on p 22 of the student’s book.
Explain that all electrical circuits need a source of energy. It may help if you think of the voltage as being
the ‘push’ which makes charge flow. A normal dry cell or a lead-acid battery provides the voltage or the
potential difference needed to make a current flow in a circuit. Voltage is measured in Volts (V) using a
voltmeter. A normal dry cell gives about 1.5V. Explain that a number of cells may be joined together to
make a battery which gives a bigger voltage. A lead-acid cell gives about 2V. A car battery uses six cells to
give a total of 12V between its terminals.
Measuring voltage
Ask the students: what is the force which drives a current in a circuit?
Explain that the driving force is called voltage. Show the students some dry battery cells and ask them to
read the voltage on them. We can measure voltage by a voltmeter.
Set up a circuit containing a voltmeter and show the students how to read it. Explain that unlike ammeters,
voltmeters are not connected in the main circuit. They are added across the component where we want to
find the voltage.
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V
V
correct
wrong
Like ammeters, voltmeters must be connected the right way round. If not, the pointer moves the wrong
way and the meter can be damaged. Draw the circuit on p 22 of the student’s book which shows how the
voltmeter is connected to the circuit.
Voltages around a circuit
Ask the students: how does a circuit get its power supply?
Explain that the battery or power supply provides the total voltage for the circuit. In a simple circuit, the
voltage across all the components adds up to the supply voltage.
For example, study the circuits shown in the diagrams.
V
3V
V
V
1V
V
3V
+
1V
+
V
1V
=
V
3V
1.5V
V
+
1.5V
=
3V
These circuits show how the voltage is ‘shared out’ when all the components, in this case lamps, are
identical.
Voltage, current, and resistance
Ask the students: what is resistance?
Explain that any electrical appliance added to a circuit offers resistance to the flow of the current. In a
circuit the power supply provides the voltage which makes the current flow. Larger voltages cause larger
currents.
3.0V
1.5V
A
0.3A
1.5V gives a current of 0.3A
4.5V
A
0.6A
Twice as much voltage (3.0V) gives
twice as much current (0.6A)
A
0.9A
Three times the voltage (4.5V) gives
three times the current (0.9A)
Resistance
Ask the students: does a battery always give the same current?
Explain that a battery does not always give the same current. It depends on what is in the circuit
connected to. Some components allow electricity to pass ‘easily’. We say that these have ‘low resistance.’
Other components make it ‘hard’ for the current to flow. We say that these have ‘high resistance’.
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The resistance of a component or a circuit tells us how many volts we need to make a current of one
ampere flow. If a circuit has a large resistance, we have to apply a high voltage to get the current of one
ampere to flow. If the circuit has a low resistance only a small voltage is needed.
Ask the students: what is resistance measured in?
Explain that the unit used for measuring resistance is an ‘ohm’. This means that 1V is needed to make a
current of 1A flow through a resistance of 1 ohm. The resistance of a component or a circuit tells us how
many volts we need to apply to make a current of 1A flow. If a circuit has a large resistance, we have to
apply a high voltage to get a current of 1A to flow. If the circuit has a low resistance, only a small voltage
is needed.
Resistance and wires
Ask the students: what are wires commonly made of? Why?
Explain that the wires used for connecting up circuits in the laboratory or in the home have very low
resistance. This is because they are made of copper; a metal which is a very good conductor.
The resistance of any wire depends on three main things: its length, its diameter or area, and the material
from which it is made.
Draw the diagram shown on page 23 of the student’s book which shows a circuit to measure the
resistance of a piece of wire. The voltmeter is measuring the voltage across the wire and the ammeter is
measuring the current in the wire.
Explain that to find the resistance we just divide the voltage by the current.
voltage
(V)
=
current (I) x resistance (R)
V
=
IR
voltage
current
=
resistance
V
I
=
R
or
Thus,
Calculation
Voltmeter reading
=
3V
Ammeter reading
=
2A
R
=
V/I
R
=
3V/ 2A
=
1.5 ohms
Additional activity 1
The diagram shows the circuit set up by a student trying to measure the resistance of a light bulb. The
student has made several mistakes. What are they? Draw the correct circuit.
V
0
+
5
+
–
0
A+
–
–
+
5
–
When the circuit is set up correctly, it is found that a voltage of 3V gives a current of 0.5A.
What voltage will be needed to give a current of 1A?
What is the resistance of the bulb in the circuit?
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Additional activity 2
A student uses the above apparatus to measure the resistance of a copper connecting wire. She finds
that 0.1V gives a current of 1A.
What is the resistance of the copper wire? Why is the girl’s value for the resistance likely to be
inaccurate? [Hint: think of the voltmeter scale.]
Controlling the current
Ask the students: do we need to control the current in a circuit sometimes? Why? How?
cell
Explain that when we need to control the current in
a circuit, we can use a resistor. The diagram shows a
resistor being used to protect a lamp which would ‘blow’ if
connected directly to the battery. Having extra resistance
in the circuit limits the current.
switch
Additional activity 3
sliding contact
Draw a graph of a current-voltage relation for a resistor,
using the table below.
Voltage across resistor
Current in resistor
0V
0.0A
1V
0.2A
2V
0.4A
3V
0.6A
4V
0.8A
lamp
resistor
What is the relation between the current and voltage through a resistor?
[Hint: current is proportional to the voltage.]
If we repeat the above experiment with a filament lamp in place of the resistor, we find that it does not
always have the same resistance.
Additional activity 4
Draw a graph showing the current-voltage relation for a filament lamp, using the table below.
Voltage across lamp
Current in lamp
0V
0.0A
1V
0.2A
2V
0.35A
3V
0.5A
4V
0.6A
What does the graph show? What does the graph show about the relation between the current and the
resistance of the filament bulb?
[Hint: a wire has a higher resistance when it is hot than when it is cold.]
Investigating electrical supplies
Show the students an oscilloscope if possible. Explain how it works. When a dry cell is connected to an
oscilloscope the trace moves up the screen but remains a straight line. This tells us that the dry cell gives
a steady, direct current.
If the cell is reversed then the trace moves down from its starting position. This is because the voltage has
been reversed.
When the output of a bicycle dynamo is connected to an oscilloscope we get a complicated pattern. The
dynamo voltage changes direction. This means that it is producing alternating current (AC).
Ask the students: what kind of voltage is supplied to our homes?
Explain that the electricity board supplies an alternating voltage to our homes. When we turn on, say, a
light bulb, the alternating voltage makes an alternating current flow in the circuit.
Explain that alternating current is expressed in terms of frequency, which is the rate at which something
occurs. Frequency is measured in hertz (Hz). In terms of electricity, we say that the frequency is one Hertz
in one cycle is complete in one second.
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Energy for everyday use
Ask the students: where does electricity in our homes, offices, schools, etc., come from?
Discuss the production methods of electricity in power stations.
Ask the students: does the power station have a bad affect on the environment? Why are overhead electric
wires and cables dangerous?
Discuss the risks that are involved in generating electricity, and its effects on the environment.
Safety and electricity
Ask the students: why is it dangerous to touch a live wire?
Explain that if you touch a live wire carrying about 220V, an electric current can pass through your body
to the ground which is at 0V. The pain you feel is an electric shock. The small current which runs through
your body may be enough to kill you, even though it is too small to blow the circuit’s fuse.
Ask the students: is there any way in which our buildings are protected from electric shocks?
Explain that ring mains and lighting circuits have an earth wire to protect users. Outside each house,
close to where the main electricity cables enter, a metal plate is buried in the ground. This is joined to a
connector block in the consumer unit where the earth wires from all the house circuits are connected. If a
fault lets the live wire become connected to the earth, a large current flows in the earth wire. This makes a
fuse blow, often with a bang, cutting off the electricity supply.
Additional activity 5
Investigating the current at which a 1A fuse ‘blows’.
The diagram shows the apparatus which can be used to find the current which will cause 1A fuse wire
to melt.
current supply
�
�
�
�
�
�
��
�
��
�
��
���
�
�
�
ammeter
1A fuse
bulb
Notice that the light bulb must be able to take a current greater than 1A or the filament may melt
before the fuse wire.
The control on the power supply is set at zero. It is then gradually increased. The current rises until the
fuse ‘blows’. If you watch the ammeter carefully, you can record the maximum current allowed by the
fuse. [Hint: the maximum current is often higher than expected.]
Residual circuit breakers
Ask the students: what might happen if an earth wire is not enough to blow a fuse?
Explain that sometimes a fault occurs which makes the outside of a properly earthed appliance become
live but where the current in the earth wire is not enough to blow a fuse. This could be very dangerous. A
residual current circuit breaker can be used to protect against this. It contains an electro-magnetic switch
which quickly turns off the power if the current in the earth wire is bigger than 0.03A. Circuit breakers like
this are recommended for use with lawn mowers and portable tools like electric drills.
No earth wire
Ask the students: do all electrical appliances have an earth wire?
Explain that appliances marked ‘double insulated’ do not have an earth wire. This is because their metal
parts are covered with insulating plastic. The live wire can never touch the casing and so cannot give the
user a shock.
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Paying for electricity
Show the students an electricity bill. Explain how we are charged for the electricity we use.
Energy is measured in units called joules (J). The power of an electric appliance tells us how many joules
of energy it converts in one second. Power is measured in units called watts (W); 1 Watt is 1 Joule in each
second.
So, for example, a 100W light bulb converts 100 J of energy in each second. The power of an appliance
used for heating is likely to be much higher and may be measured in kilowatts (kW). Remember that
1kW = 1000W.
Additional activity 6
Try to find the power of the following household appliances: an electric kettle, an iron, a tumble drier,
a toaster, a vacuum cleaner, an electric drill, a stereo music system, and a table lamp.
What do you notice about the power of appliances which contain a heating element compared with the
power of those used to produce sound and light?
The longer an appliance is turned on, the more energy it will ‘use’.
A 1kW heater switched on for one hour will use 3 600 000 J of energy (1000W x 3600 seconds). Such
numbers are very difficult to work with, so the electricity board calculates the energy used in ‘units’ called
kilowatt hours (kWh).
A 1kW appliance turned on for 1h will convert 1kWh of energy. It is easy to work out how much an
appliance costs to use if you know the cost of 1kWh.
energy used
=
power
(kWh)
cost
x
time
(kW)
=
energy used
(h)
x
cost of 1kWh
The amount of electrical energy used in the home is measured by a meter. When current flows through the
meter the numbered dials move. These show how much energy has been used. The cost of the electricity
that has been used can then be calculated by the number of units consumed.
Answers
Energy and electricity: p 20
1.
Chemical energy, electrical energy, light energy, sound energy, kinetic energy, potential energy.
2.
a)
Fuel is burnt to heat water in the boiler of the steam engine.
b)
The alarm clock is powered by winding up a spring until it is tightly coiled.
3.
Heat energy
4.
a)
The energy used to make things move is called kinetic energy. For example, a moving car has
kinetic energy; all moving objects possess kinetic energy.
b)
The kind of energy that a body possesses due to its position is called potential energy. For
example, when a spring or piece of elastic is stretched, it has potential energy.
Similarly, the energy possessed by a body that has been lifted up is called ‘gravitational potential
energy’.
5.
A telephone changes sound energy into electrical energy and then back into sound energy.
6.
The wind-up radio generates its own electrical energy simply by turning a handle, which powers the
radio.
Energy arrows: p 21
1.
A Sankey diagram is a simple way of showing what energy changes take place and where energy goes.
It looks like a set of arrows.
2.
The width of the arrows gives an idea of the amounts of the different forms of energy; the thicker
the arrow the greater the amount of energy.
3.
It means that only about 80% of the electrical energy is converted into light energy; the rest is wasted
as heat energy.
4.
Most energy is lost from the boiler when fuel is burnt to heat water to turn it into steam.
5.
a)
electrical energy to kinetic energy
b)
electrical energy to heat and light energy
c)
electrical energy to mechanical and sound energy
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6.
sound
heat
movement
Power supplies and voltage: p 22
1.
a)
The driving force of a current is called voltage.
b)
Volt (V)
2.
4.5V
3.
voltmeter
4.
The voltmeter should be connected in parallel with the bulb to measure the difference in the driving
force from one side of the bulb to another.
5.
She had connected the voltmeter in series with the circuit. It should have been connected in
parallel.
Resistance: p 23
1.
The slowing down or stopping of the flow of electricity is called a resistance.
2.
A current flowing through a resistance wire produces a heating effect. If it is too great, the filament
(the thin wire inside the bulb) melts and breaks.
3.
a)
ohm
4.
a)
6V
b)
Ohm’s law
b)
Ω
voltage (V) = current (I) x resistance (R)
resistance
= voltage/current
= 3V / 0.5A
= 6 ohms
Controlling the current: p 24
1.
2.
A resistor can be used to control the flow of current in a wire.
3.
A variable resistor can change the current in a circuit. It has a sliding contact. As the contact is moved,
the length of the resistance wire connected in the circuit changes and so the current changes.
4.
The current is proportional to the voltage.
5.
As voltage is directly proportional to the current we would need a very large graph paper.
Electricity in the home: p 25
1.
32
a)
Mains electricity is produced at power stations by the electricity generating board.
b)
It is sent along power lines to houses, factories, hospital, schools, and other users.
2.
The mains supply can supply very large currents. Touching them could give you a fatal electric
shock.
3.
The mains voltage changes very rapidly. This makes the current flow backwards and forwards 50
times in each second. This is called an alternating current or AC with a frequency of 50 Hz.
4.
a)
2
b)
One is called the live wire and the other is called the neutral wire.
c)
The live wire is at about 230 volts and the neutral wire is at about 0 volts.
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5.
a)
Hz stands for hertz. It is used to measure frequency.
b)
1 Hz is one cycle completed in one second.
Safety and electricity: p 26
1.
A consumer unit consists of all the fuses that connect the electricity meter to all the electrical circuits
in the house.
2.
It is important to use the correct fuse to replace the one that is blown because if it is rated at too
high a current, it could allow an overload to cause damage without melting and blowing.
3.
a)
mcb means a miniature circuit breaker
b)
rccb means a residual current circuit breaker
4.
Fuses are always connected to the live wire so that they can be used to disconnect the appliance from
the mains supply.
Choosing the correct fuse: p 27
1.
a)
The main fuses in the consumer unit protect the house circuits from damage due to too much
current.
b)
Each appliance can be protected by a fuse in its plug. If the current gets too great, the fuse wire
melts and breaks the circuit.
2.
3A, 5A, 13A
3.
They are colour coded so that they can be recognized easily even by a person who needs reading
glasses.
4.
a)
1500/250 = 6A
A 13A fuse (brown) would be suitable.
b)
200/250 = 0.8A
A 3A fuse (red) would be suitable.
Paying for electricity: p 28
1.
The greater the power, the quicker the appliance takes energy from the mains.
2.
Electricity generating boards measure electrical energy in kilowatt hours (kWh). For example, if a 1
kW toaster is switched on for 1 hour, then 1kWh or 1 unit of energy is supplied.
3.
a)
2kW x 4h = 8 kWh x Rs 4 = Rs 32
b)
100/1000kW x 5h = 0.5kWh x Rs 4 = Rs 2
c)
1/1000 x 4 = 0.004kWh x 4 = Rs 0.016
4.
Appliances containing a heating/cooling element use up more power as compared to those which
produce sound or light.
Energy for everyday use: p 29
1.
a)
oil, gas, water, coal, nuclear fuel
b)
coal
2.
It is generated in power stations by using an energy source.
3.
Electricity is made in power stations. Coal is used to heat water to produce steam. This steam is used
to turn steam turbines which then turn the generators that produce electricity. Power stations convert
heat energy of burning fuel into mechanical energy which rotates the turbines. Mechanical energy of
the turbines is used to turn the generators which produce electrical energy.
4.
Potential energy in the water, stored high up in the mountains, is converted into kinetic energy of
flowing water which is then converted into mechanical energy to turn the turbines. Mechanical energy
from the turbines turns the generators, which change mechanical energy into electrical energy.
5.
Water is a renewable energy source. It can supply energy for millions of years without being exhausted.
The other energy sources such as oil, gas, coal and, nuclear fuel (plotonium and uranium) have been
made under the Earth millions of years ago. Once they are used up they cannot be remade very
quickly.
Energy production: the bad news: p 30–31
1.
This means that only about 35% of energy in its fuel is changed into electrical energy.
2.
a) heat
3.
a)
Fossil fuels are fuels like coal, gas, and oil which were produced inside the Earth millions of years
ago from the bodies of plants and animals.
b)
Burning fossil fuels produces carbon dioxide and acid rain.
b) mechanical and heat
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4.
a)
Warm water in a power station comes from the turbines.
b)
Increased water temperatures can cause serious changes to the ecosystems. Many animal and
plant species will be affected adversely. Food chains and food webs will be destroyed. Many
organisms will die.
Test yourself: p 32
1.
2.
a)
electrical‡ heat and light
b)
electrical ‡ mechanical and sound
c)
electrical ‡ heat and light
d)
electrical ‡ mechanical and sound
e)
chemical ‡ electrical
f)
light ‡ mechanical and electrical
a)
12V
b)
+
–
c)
-
+
V
3.
a)
3V
2A
A
b)
The current flows directly to the bulb through the closed switch, instead of passing through the
resistance.
c)
resistance = voltage/current
= 3V / 2A
= 1.5 ohms
4.
a)
energy used in kWh = power in kW x time in hours
= 2kW x 5/60h
= 1.66kWh
b)
The cost to boil water in the kettle:
1.66kWh x Rs 4 = Rs 6.64
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c)
Power of kettle = 2kW
= 2000W
Time taken to boil the water = 5 minutes
= 5 x 60
= 300 seconds
Power is defined as Joules per second.
Therefore, Joules
= power x time
= 2000 x 300
= 600 000 J
5.
a)
i) Potential energy
ii) Kinetic energy
b)
i) Turbines
c)
Water is a renewable energy source.
ii) Heat energy warms the water coming out of the power station.
Pollution of the environment is reduced to the minimum.
6.
a)
In turbines
b)
As heat
c)
Electrical output: in X = 5600 – (600 + 2900 + 40 + 60)
= 5600 – 3600
= 2000MW
Electrical output in Y = 5600 – (200 + 3800 + 40 + 60)
= 5600 – 4100
= 1500MW
d)
Power station X is more efficient because it produces more megawatts of electrical power for the
same amount of power input from the fuel (coal) being used.
Workbook 3, chapter 3
1.
a) C
2.
a)
b) B
c) D
d) A
i) electrical energy ‡ sound energy
ii) electrical energy ‡ light energy
iii) electrical energy ‡ heat energy
b)
Escapes as heat energy
c)
heat
light
3.
4.
sound
a)
i) 3V
ii) 3V
iii) 3V
b)
i) zero
ii) zero
iii) zero
c)
The pointer moves the wrong way and the meter may be damaged.
a)
Resistance is the measure of how different materials resist the flow of electricity through them.
b)
Resistance is measured in units called ohms.
c)
resistance (R) = voltage (V)/current (I)
iv) 9V
= 6V/ 4A = 1.5 ohms
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5.
a)
current in amps
0.8
0.6
0.4
0.2
0
b)
i)
0.7A
ii)
0.5V
1
2
3
voltage in volts
c)
The current doubles
d)
resistance (R) = voltage (V)/current (I)
4
5
= 1V / 0.2A = 5 ohms
6.
a)
i) 20W
ii) 100W
b)
kWh is a unit of electricity, which is used to measure the amount of electrical energy an electric
appliance can use up in an hour.
c)
energy in kWh = power in kilowatts x time in hours
= 20/1000kW x 1000 hours
= 20kWh
d)
energy in kWh = 100/1000kW
x 1000 hours
= 100kWh
e)
cost of using the low energy bulb = 20kWh x Rs 4 = Rs 80
cost of using the high energy bulb = 100kWh x Rs 4 = Rs 400
Saving on electricity bills will be 400 – 80 = Rs 320
7.
Electricity is made in power stations. Most countries make their electricity using the chemical energy
in fossil fuels, and the nuclear energy in uranium. Power stations which convert the energy from
fuels into electrical energy are called thermal power stations.
Thermal power stations waste more energy than they produce. The efficiency of a typical coal burning
power station is only about 35%. Burning fuels like coal produces carbon dioxide and causes acid
rain. Water from power stations, warmed during energy production, is often dumped into the local
river, or the sea. Increased water temperatures can cause serious changes to these ecosystems.
Project
Varying resistance
You will need: battery, 3 leads, bulb, soft pencil.
Strip the wood from the pencil after soaking in water. Attach wires to the bulb and battery terminals and
connect the bulb and battery. Touch the pencil lead with the free ends, close together but not in contact.
The bulb should light up. Move the wires apart so that there is more pencil lead in the circuit, increasing
the resistance and making the bulb dimmer.
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Multiple Choice Questions
1.
Which type of energy is not produced by a television set?
A chemical energy
2.
A copper
3.
4.
C sound energy
B nichrome
D heat energy
C iron
D steel
Which of the following is most likely to be the hottest when the same amount of current is passed
through them?
A a thin and short wire
B a thin and long wire
C a thick and short wire
D a thick and long wire
The rating of fuse wires in household circuits are marked in
A amperes
5.
B light energy
Which of the following will give the least resistance to a current if they are made into wires of the
same diameter and length?
B volts
C watts
D ohms
Which statement is wrong?
A a 13A power plug has a fuse
B a three pin power plug usually has an earth wire
C the wires in a house are usually connected in series
D the wires in a house are usually connected in parallel
6.
Fuses in the consumer unit are put in the:
A earth wire
7.
B live wire
C neutral wire
D resistance wire
Which of the following statements is correct about a fuse?
A it prevents the current from increasing
B it helps lower the resistance in a circuit
C it prevents parts of a circuit from being damaged by extra current
D it helps to increase the brightness of bulbs in a circuit
8.
Which source of energy is least used to generate electricity?
A oil
9.
B gas
C coal
D nuclear fuel
C oil
D gas
C watt seconds
D kilowatt seconds
Hydro electricity is produced from
A coal
B water
10. Electricity generating boards measure energy in
A watt hours
B kilowatt hours
Answers
1.
A
6. B
2. A
3. B
4. A
5. C
7.
8. D
9. B
10. B
C
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Fit and healthy
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Unit flow chart
Healthy eating
Malnutrition and deficiency diseases
Drugs
Keeping fit and healthy
Aims and learning objectives
•
To describe how the body uses energy in food
•
To describe some of the results of malnutrition
•
To describe some of the effects on the body of smoking and other harmful drugs
•
To be able to explain why exercise is good for the body
Background information
The food we eat provides our bodies with stores of chemical energy. Most of this is used to provide energy
for four things:
1. to keep our bodies working
2. for growing new cells in our bodies
3. to keep our bodies at the right temperature
4. to enable our muscles to do work
Keeping a healthy body weight is a matter of balancing the energy we take in as food, with the energy we
use up. Any unused energy is stored as fat in our bodies.
Starchy foods are first converted by digestive enzymes into sugars such as glucose. The chemical
breakdown of glucose to release energy takes place inside the body cells. This process is called
respiration.
We can keep fit by eating reasonable amounts of sensible foods, and by exercising regularly.
Unit introduction
Ask the students: what do all machines need to work properly? What is the fuel used by a machine? What
is the fuel needed by our bodies to work properly?
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Explain that like all machines, the human body requires a constant supply of fuel and enough materials for
repairs.
Ask the students: what is the fuel for the human body? Where does this fuel come from?
Explain that food supplies energy and all the chemicals needed for growth and to keep the body working
properly.
Ask the students: which foods provide us with energy?
Explain that all foods except vitamins and minerals contain stored energy. This energy is released and
made available to living things during the chemical reactions of respiration.
Ask the students: what is respiration? How does respiration help to release energy?
Explain that when food is burned it releases the same amount of energy in the form of heat, as it does
when respired.
Teaching procedure
Discuss what the students eat for breakfast, lunch, and dinner.
Count the number of children who have a healthy balanced diet and those who are undernourished or
overweight. Discuss the constituents of a healthy diet and the use of each constituent in the body.
Types of food and their composition
Ask the students: what foods do they take for breakfast, lunch, and dinner. Also what kinds of snacks do
they like.
Discuss the importance of the different types of food and their use in the body.
Carbohydrates are found in sugary and starchy foods such as sweet fruits, honey, jam, bread, cakes,
potatoes, rice, and spaghetti.
Carbohydrates are the main source of energy for living things. One gram yields about 17kJ of energy
during respiration. Most carbohydrates are converted into glucose before they are respired.
Fats and oils are also known as lipids and include butter, vegetable oil, olive oil, etc. These are important
sources of energy because 1g of lipid can yield up to 38kJ of energy when respired. But they are less
easily digested than other foods. Fats are important for energy storage in animals and plants.
Proteins are commonly found in meat, liver, kidney, eggs, fish and beans. These foods supply the raw
materials living things need for growth and for the repair of damaged and worn-out tissue. Proteins are
not usually respired for energy, but when this happens they can yield up to 17kJ of energy per gram.
Vegetarian diets and protein deficiency
Ask the students: what do vegetarians eat? How many of you dislike meat? What kind of food is meat?
What happens to the proteins that we eat?
Explain that proteins are digested into chemicals called amino acids. There are about 26 of these but only
10, called essential amino acids, are needed by humans. Our bodies can make the rest. Animal proteins
contain all ten essential amino acids, and so are called first-class proteins. No single plant protein contains
all the essential amino acids, so they are called second-class proteins. However, all 10 can be obtained by
eating a wide variety of plant foods.
A vegetarian diet can be extremely healthy because it does not usually contain excessive amounts of fat,
sugar or salt, and is high in dietary fibre.
Ask the students: why do we take vitamins and minerals?
Explain that the chemical reactions that take place in your body need vitamins and minerals to control
them. Vitamins are substances with no energy value, but which are essential for growth and health. Some
are needed in very small amounts—less than one millionth of a gram a day. There are 13 major vitamins.
They take part in the chemical reactions of metabolism, usually in conjunction with enzymes. Vitamin A for
example, helps to prevent infection. Vitamin C helps the body to absorb iron, which forms an important
part of your red blood cells. Vitamin D helps the body use calcium and phosphorus to make teeth and
bone tissue. Most vitamins come from fruit and vegetables. Shortage of vitamins in the diet causes
diseases like scurvy and rickets.
Minerals, like vitamins, have no energy value but are essential for health. You require about 15 different
minerals in your diet. Most essential minerals are supplied by a diet of meat, eggs, milk, green vegetables,
and fruit.
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Additional activity 1
Make a food chart
Food
Source
Use in the body
Effects of deficiency
proteins
fats
carbohydrates
vitamin A
B
C
D
E
K
minerals
iron
calcium
salts
water
Ask the students: why is water very important for our body?
Explain that water is needed by our body as the solvent to enable all the chemical reactions to happen.
You can live several weeks without food, but not without water even for a few days.
Ask the students: what kind of a diet must we take?
Explain that a balanced diet is one which contains the right amounts of protein, carbohydrate, fat,
vitamins, and minerals to satisfy all your body needs.
Additional activity 2
Write the name of the food under the correct heading: lettuce, beef, cornflakes, chicken, potato crisps,
baked beans, eggs, apples, grapes, cheese, milk, yoghurt, bread, fish, peanuts, rice.
Protein
Carbohydrate
Fat
Malnutrition
Ask the students: what will be the effect on our bodies if we do not eat a varied diet?
Explain that if we do not eat a varied diet in the right proportion, we will be under-nourished. This is
called malnutrition which means bad nutrition, but the word usually refers to the effects on the body of
eating too much, too little or the wrong kinds of food.
Ask the students: what effect would overeating have on the body?
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Explain that eating too much can cause a person to become fat or obese. There is now clear evidence that
obesity contributes to heart disease, high blood pressure, diabetes, diseases of the gall bladder, cancer of
the bowels, and breast cancer in women.
Discuss the harmful effects of smoking and drinking alcohol. Some people may be unlucky and may have
a serious disease through no fault of their own. Others make it more likely that they will become ill by
smoking or drinking too much alcohol. A few people risk their health even more by taking harmful illegal
drugs.
Smoking
Ask the students: whose father or grandfather smokes?
Discuss the bad effects of smoking. Explain that nearly 100,000 people a year die prematurely from
smoking-related diseases such as cancer, heart disease, and bronchitis. Young smokers, who give up,
greatly reduce their chances of developing these diseases.
Diseases caused by smoking
Heart disease is three times more common among smokers than among non-smokers.
Emphysema is a disease in which lung tissue is destroyed by the chemicals in tobacco smoke. Cancers of
the lungs, mouth, gullet, and bladder are caused by the chemicals in tobacco smoke.
Bronchitis is mostly a smoker’s disease. The cilia which line the air passages in the lungs stop working and
the lungs fill up with mucus.
Passive smoking
Ask the students: how are people who do not smoke affected by living and working with smokers?
Explain that non-smokers who live and work with smokers can suffer lung damage and other smokers’
diseases. Many non-smokers find tobacco smoke very unpleasant. It makes eyes sting and can cause sore
throats and headaches. It can irritate babies and people with hay fever and asthma.
Smokers smell. Their breath, hair, clothes, and homes have a horrible smell, caused by the ammonia, tar,
and other chemicals in smoke.
Additional activity 3
Work out how much it costs to buy 20 cigarettes a day for a year. List the things a person could buy if
he saved this amount by giving up smoking.
Alcohol
Discuss the harmful effects of drinking alcohol. Explain that alcoholic drinks like beer and wine contain
ethanol. This is absorbed into the blood stream and carried into the brain. A little ethanol makes people
relaxed, but too much can cause them to lose control over their speech, movements, and emotions. High
levels of ethanol in the blood can cause unconsciousness and even death. The liver treats ethanol as a
poison and works hard to break it down. If a person drinks heavily for some time, he risks liver and heart
disease, brain damage, and cancer of the digestive system.
Illegal drugs
Ask the students: what are drugs? What are illegal drugs? What are the harmful effects of taking drugs?
Explain that cocaine, LSD, and cannabis are illegal drugs. Morphine, tranquillisers, and barbiturates are
medicinal drugs, available on prescription, but they are illegal if not prescribed to the user.
The various drugs are smoked or injected into the bloodstream. In each case, the chemical is absorbed
into the blood and carried to the brain. Short-term risks include having accidents while under the influence
of the drug, while overdoses may prove fatal. Brain damage can result from long-term use. But perhaps
the most dramatic effect drugs have is the way they can completely take over a person’s life. Drug addicts
become physically addicted to a drug and may commit crimes to obtain money to buy the drug.
At one time, cannabis was thought to be less dangerous than many other drugs. However, recent research
has shown that it can cause memory loss and can be addictive. Long-term effects can include permanent
loss of brain function and cancer of the tongue, throat, and lungs.
Discuss the effects and risks to human health of taking drugs. Explain to the students that a drug
overdose can cause unconsciousness, damage to the heart and other organs, and even death. A drug user
may suffer strong feelings of anger and fear or terrifying hallucinations.
Drug users become irritable and lose interest in their friends, family, hobbies, and work. They may stop
looking after themselves. People taking drugs also run the risk of accidents, because they get confused.
They can fall into water and drown, or walk in front of traffic, or fall out of windows.
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Additional activity 4
Make a chart about:
Things that can lead to heart disease:
Eating lots of fat
Cigarette smoking
Obesity
No exercise
Stressful way of life
How heart disease can be avoided
•
Cut down on fried foods
•
Eat less red meat
•
Eat less dairy foods
•
Eat more poultry and fish
•
Eat more fresh fruit and vegetables
•
Do not smoke
Exercise regularly
Take time to relax and think. In the future you may be offered cigarettes, alcohol and possibly even illegal
drugs. You will have to make the decision, but you know that all these things contain chemicals to which
you may become addicted. They can all damage your health.
Friends who think less of you because you do not want to smoke, drink or take drugs are not real friends.
Answers
Fit and healthy: p 34
1.
Adults are not growing any more. Their bodies may become fat. They need to exercise to maintain
a healthy body. Children are growing so they need more food and energy and hence they need to
exercise more.
2.
Good health is when you feel good both physically and mentally.
3.
A healthy mind helps you to cope with the many challenges that life throws at you.
4.
We can ensure good health by:
•
eating a balanced diet
•
exercising regularly
•
not abusing our body with drugs.
Healthy eating: p 35
1.
Each year a human being eats over 1 tonne (1000 kg) of food and drinks about 500 litres of liquid.
2.
A balanced diet should contain:
•
foods that provide energy
•
foods that provide building materials
•
foods that control chemical reactions
•
foods that contain dietary fibre.
3.
A person becomes fat or obese by eating too much energy foods. These contain fats and sugars.
If the energy provided by these foods is not used up, the body stores excess energy as fat and the
person becomes over weight.
4.
Too much salt can cause high blood pressure.
5.
a)
Fibre or roughage is made up of plant cells which pass through the digestive system, without
being digested and absorbed.
b)
Fibre is important because it gives the muscles in the walls of the digestive system something
to push on. Food containing a lot of fibre helps prevent constipation and other disorders of the
digestive system such as piles.
Eating disorders: p 36
42
1.
diabetes and arthritis
2.
a)
Leafy vegetables such as spinach and citrus fruits.
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3.
b)
A disease called scurvy is caused by too little vitamin C. Scurvy causes bleeding of the gums,
loose teeth, muscle weakness and eventually death.
a)
Rickets is a disease which affects bones, making them soft so they become bent and twisted.
b)
Rickets is caused by the deficiency of calcium or vitamin D in the body.
4.
A person affected with anaemia looks pale and feels weak and tired.
5.
a)
Kwashiorkor is a disease caused by deficiency of proteins in the diet.
b)
A child with kwashiorkor may not have received enough of his/her mother’s milk and may have
been forced on to a high carbohydrate diet too early.
Drugs: p 37
1.
Drugs are substances that change the way the body works. They can act on the nervous system by
affecting the movement of nerve impulses along the fibres of nerve cells.
2.
Pain killers are drugs which are used for headaches and other pains. They can be bought at the
chemist. Tranquillizers are drugs that calm people down. They should only be obtained on prescription
by a doctor.
3.
Anaesthetics are drugs that are used to numb parts of the body.
4.
A drug addict is a person who uses drugs to give pleasant short-term effects.
5.
a)
A stimulant is a drug which speeds up the nervous system. For example, caffeine is a mild
stimulant, found in tea and coffee.
b)
A depressant drug slows down the nervous system; examples include alcohol, barbiturates, and
heroin.
c)
A hallucinogen is a drug that makes people feel ‘larger than life’, for example, Ecstasy and
LSD.
Smoking: p 38
1.
nicotine, tar, carbon monoxide, cyanide
2.
Nicotine in the tobacco is an addictive drug.
3.
Chemicals in tobacco smoke kill the cilia which clean the lungs. The lungs can quickly be affected by
bacteria. This causes bronchitis.
4.
lung cancer and emphysema
5.
Pregnant women who smoke have smaller babies because carbon monoxide gas produced by smoking
prevents sufficient oxygen reaching the baby in the womb, upsetting its growth. Childbirth can also
be difficult.
Keeping fit and healthy: p 39
1.
Due to developments in medical care fewer people are dying of infectious diseases and more are living
longer.
2.
Improved transport, home entertainment, computer games, and labour saving devices around the
home and garden.
3.
Endorphins are happiness chemicals which help to lower anxiety and increase the feeling of well-being
and make the body feel relaxed.
4.
Brisk walking moves more oxygen into the brain and triggers the release of endorphins into the bloodstream.
5.
Regular exercise helps the body to be fit and healthy.
Test yourself: p 40–41
1.
2.
3.
a)
i) OK
ii) very fat, treatment required
b)
His health would suffer if he did not lose weight.
a)
i) scurvy
b)
i)
A person affected with anaemia looks pale and feels weak and tired.
ii)
The bones of a person affected by rickets are bent and twisted.
ii) rickets
iii) anaemia
iii) overweight
iv) underweight
iv) kwashiorkor
a)
The graph shows that the risk of dying from lung cancer is increased with the number of cigarettes
smoked per day.
b)
i)
c)
Smoking can damage one’s health because tobacco smoke contains many harmful chemicals like
nicotine and tar. It also contains harmful gases like carbon monoxide, ammonia, and cyanide.
more than 5 times
ii) more than 30 times
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4.
5.
d)
Young people should be advised by their teachers and parents about the harmful effects of
smoking cigarettes. They should be encouraged to eat healthy foods and take plenty of exercise.
They should play outdoor games, ride bikes or work out at gyms. They should not try smoking
a cigarette even if it is for fun, as it can become an addiction. (Students should give their own
suggestions as well.)
a)
It is a painkiller and does not cause addiction.
b)
They are strong stimulants and can cause addiction.
c)
It is an addictive depressant.
d)
The user will see horrifying things and become very scared.
e)
All drugs are not dangerous. Some drugs like painkillers are useful in relieving pain. But some
drugs are addictive and if taken in large doses can be very dangerous for the body.
a)
Energy value means the amount of energy that a certain food will provide to the body when
eaten.
b)
Meal 1: 540kJ
c)
Meal 1
d)
It could cause deficiency diseases in the body.
Meal 2: 2260kJ
Workbook 3, chapter 4
1.
a)
Breakfast 1 = 780kJ
Breakfast 2 = 1560kJ
b)
A building site worker needs more energy than an office worker.
c)
They have fats.
d)
i)
Food containing a lot of fibre helps prevent constipation and other disorders of the digestive
system.
ii)
Breakfast 2
iii) Porridge and bread contain a lot of fibre as they are made of cereals.
2.
A person who eats too much becomes fat or obese and is at risk from a number of serious diseases
such as diabetes and arthritis. A person who eats too little however, becomes malnourished. This
can cause deficiency diseases. A disease called rickets causes bones to develop incorrectly. Vitamin
D is needed by the body to develop strong bones.
Leafy vegetable such as spinach and citrus fruits such as oranges and lemons contain vitamin C. A
disease called scurvy is caused by too little vitamin C.
A deficiency of iron causes a disease called anaemia.
The most obvious sign of malnutrition is often caused by lack of protein in the diet. A disease caused
by this deficiency is kwashiorkor.
3.
44
Drug
Effect
alcohol
depressant that causes dehydration and liver damage
heroin
speeds up the heart rate. Longer term, it damages nerves
nicotine
narcotic, with numbing properties
cannabis
stimulant that speeds up everything
Ecstasy
mild hallucinogen which relaxes muscles
caffeine
mild stimulant that increases concentration
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a)
30
Deaths per 10000 men
Deaths per 10000 men
4.
20
10
10
5
0
10
20
30
40
Number of cigarettes smoked per day
0
5
10
20
15
Number of years stopped smoking
b)
i) 21
c)
i)
The death rate increases with the number of cigarettes smoked per day.
ii)
The death rate decreases with the number of years men stopped smoking.
d)
ii) 4
Gases such as ammonia and cyanide irritate the insides of the air passages. This causes smoker’s
cough.
5.
swimming, boating, cycling, playing football, riding a scooter, skating, jogging, walking, sitting in the
open air, playing on the slide
6.
eating fast foods, smoking, drinking cola, eating junk food, watching TV while lying down, putting
food on the floor, keeping food in open cupboards, slouching in front of the computer, doors and
windows closed.
Project
Make a poster: SAY NO TO DRUGS and display it in the school corridor.
Multiple Choice Questions
1.
Which of the following is a kind of sugar?
A butter
2.
A cooked rice
3.
6.
8.
B egg white
C butter
D milk
B hair
C nails
D red blood cells
B calcium
C iron
D iodine
The use of proteins in our diet is to
A produce energy
B build muscles
C supply nitrogenous wastes
D help digestion
Which of the following does not contain vitamin C?
A apples
7.
D glucose
Anaemia may be caused by the deficiency of
A sodium
5.
C milk
Iron is needed in the body for the formation of
A meat
4.
B meat
Which of the following contains a lot of starch?
B oranges
C cod liver oil
D
green vegetables
Vegetables should be included in our daily diet because they
A provide us with a lot of energy
B produce enzymes
C activate movement of the intestines
D consist of important materials for body-building
LSD is a drug which is a
A stimulant
B depressant
C anaesthetic
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9.
Nicotine in cigarette smoke is a poison which
A causes cancer of the mouth
B damages the heart and nerves
C prevents the blood from carrying oxygen around the body
D causes lung cancer
10. Which one of the following does not ensure good health?
A eating a balanced and varied diet
B exercising regularly
C smoking regularly
D not abusing your body with drugs
Answers
1.
D
6. C
46
2. A
3. D
4. C
5. B
7.
8. D
9. B
10. C
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Patterns of reactivity
Unit flow chart
How do materials react?
The reactivity series
Displacement reactions
Metals from the Earth
Extracting metals from their ores
Corrosion
Aims and learning objectives
•
To identify and describe similarities in chemical reactions between metals and oxygen, water, and acids
•
To establish and use a reactivity series for metals
•
To show that metals are extracted from the Earth as ores
•
To show why metals corrode and how corrosion can be prevented
Background information
There are 105 different elements. Of these, 84 are metals and the rest are non-metals. Metals are usually
strong. They do not break easily. They can be hammered into different shapes without breaking. They can
be drawn out to make wires. They make a ringing noise when you strike them. They are shiny. They are
good conductors of heat and electricity. They have high densities. They react with oxygen to form oxides.
When metals form ions, the ions are positive.
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No two metals have exactly the same properties. Iron has all the properties mentioned above, but unlike
most other metals, it is magnetic.
Sodium is quite different. It is so soft that it can be cut with a knife. It melts at only 98°C. It is so light
that it floats on water, but it reacts immediately with the water forming a solution. Gold unlike other
metals does not form an oxide. It is very unreactive, but it is malleable and ductile, and looks attractive,
so it is used for making jewellery.
By comparing the reactions of metals with oxygen, water, acid, metal oxides, and solutions of metal salts,
we can arrange metals in order of reactivity. This list is called the reactivity series.
Unit introduction
Ask the students: what happens to an iron nail if left outside in the garden for a few days?
Explain that it will react with the oxygen in the air and will form iron oxide which is called rust.
Teaching procedure
Take the students to the laboratory and show them a few chemical reactions of metals with water. Explain
the various reactions with chemical equations on the board.
Reaction of metals
Ask the students: why must we know how metals react with different things such as air, water, acids etc.?
Explain that knowing about the chemical reactions of metals is vital when working out how to use them.
For example, knowing how a metal reacts with dilute acids can help us decide what metal to make a can
out of. (The can may be used to store fruit, which contains natural weak acids.) How easily a metal is
attacked by the oxygen in the air tells us how quickly a metal will corrode.
Reaction of metals and water
The more reactive metals such as sodium react violently with cold water, giving off hydrogen gas and
forming an alkali, sodium hydroxide.
Metal + water/steam ‡ metal oxide/hydroxide + hydrogen.
Metals which are less reactive such as zinc and iron react very slowly with cold water, but react vigorously
with steam. Other less reactive metals such as silver do not react with water or steam.
Additional activity 1
Fill in the table to show how the following metals react with water.
Metal
Reaction
Products
Order of reactivity
potassium
sodium
calcium
magnesium
zinc
iron
copper
Reaction of metals with oxygen
Many metals react slowly with the oxygen in the air. Moist air causes some metals to corrode. However, if
metals burn in oxygen the reaction is much faster. Oxidation takes place when metals burn in air.
metals + oxygen ‡ metal oxide
Additional activity 2
Take a small piece of sodium in a combustion spoon and heat it over a Bunsen flame.
Does the sodium melt?
Does it catch fire?
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Now plunge the burning sodium into a jar of oxygen. What happens?
What colour is the flame?
Repeat the same steps for other metals like magnesium, iron, and copper.
Record your results in the table below:
Metal
Behaviour
Products
Order of reactivity
sodium
magnesium
iron
copper
Explain that metal oxides are basic oxides. Most metal oxides do not dissolve in water. However, oxides of
sodium or potassium dissolve in water to form alkalis.
Reaction of metals with acids
Write an equation of an acid reacting with a metal on the board.
Ask the students: what happens when a metal reacts with an acid?
Explain that when a metal reacts with a dilute acid, hydrogen gas is given off and a salt is formed.
magnesium + sulphuric acid ‡ magnesium sulphate + hydrogen
Magnesium reacts very quickly with the acids found in the school laboratory.
Ask the students: do all metals react as quickly with acids as magnesium?
Explain that all metals do not react with acids very quickly. Sometimes metals react very slowly with weak
acids, over many years. Acid rain attacks some metals quite severely.
Ask the students: what kind of a reaction is it? Where has magnesium gone? What has happened to the
hydrogen?
Explain that such reactions are called displacement reactions.
When a metal reacts with an acid, it replaces the hydrogen atoms in the acid to form a salt. For example,
when magnesium reacts with dilute hydrochloric acid, magnesium chloride solution and hydrogen gas are
formed.
Make a chart of the reactivity series and display it in the class.
Explain the position of the metals in the reactivity series and that it is possible to compare the reactivity
of the metals by their reaction with dilute acids. Not all metals react with acids, so displacement reactions
can be used instead to work out the order of reactivity. If a more reactive metal is placed in a solution
containing metal ions which are less reactive, then the more reactive metal will displace the less reactive
one.
For example, if magnesium is placed in a copper sulphate solution, the magnesium will displace the
copper from the solution. Red-brown copper is seen which settles on the bottom of the container.
However, if a piece of copper was placed in a solution containing magnesium ions, there would be no
reaction.
Study the table on page 45 of the student’s book and discuss the displacement reactions.
Additional activity 3
Take the students to the laboratory and show them the reactions of some metals with dilute
hydrochloric acid. Tell them to record their results in the table below.
Metal
Reaction with HCl
Products
Order of reactivity
magnesium
zinc
iron
lead
copper
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Compare this table with the previous two tables. Is iron always more reactive than copper? Is magnesium
more reactive than iron?
Displacement reactions
Ask the students to study displacement reaction on p 45 of the student’s book. Explain that here iron
and copper are competing to be the compound in the solution. Here iron wins. It drives out or displaces
copper from the copper(II)sulphate solution. Green iron(II)sulphate is formed.
In the same way other metals displace less reactive metals. This means that a metal will always displace a
less reactive metal from solutions of its compounds.
Additional activity 4
Place a coil of copper in a solution of silver nitrate.
What happens to the copper wire?
What happens to the colour of the solution?
What happens to the wire now?
Which metal is more reactive?
[Hint: check the reactivity series on page 45 of the student’s book to see if you are right.]
Metals from the Earth
An ore is a rock or mineral that contains a metal (usually in the form of an oxide). Most of the metals in
use today are found combined with other chemicals as ores in the Earth’s crust.
Name of ore
metal it contains
haematite
iron
chalcopyrite
copper and iron
malachite
copper
litharge
lead
galena
lead
bauxite
aluminium
alumina
aluminium
Extracting metals from their ores
There are three main stages in obtaining metals from their ores:
•
mining
•
extraction
•
purification
A few unreactive metals are found uncombined with other elements. For example, gold is mined straight
from the ground.
Extraction methods
There are three main methods of extracting pure metals from their ores:
•
Electrolysis
•
Reduction
•
Roasting in air
The very reactive metals such as sodium and aluminium require a great deal of energy to separate them
from their compounds. Electrolysis is used for these. It is also a very costly process because it uses a lot
of energy. Less reactive metals can be extracted by cheaper methods such as reduction.
Reduction is a chemical reaction which involves taking away the oxygen or other similar element from a
compound. Metals such as iron and lead are extracted using reduction.
Copper and mercury are extracted from their ores by roasting them in air. Some copper is found
uncombined, but most copper is found in chalcopyrite (copper(I)sulphide, also called copper pyrites).
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other metals & non metals 1%
magnesium 2%
potassium 2%
sodium 3%
calcium 4%
iron 5%
aluminium 8%
oxygen
47%
silicon
28%
Elements in the Earth’s crust
Discuss the methods of extraction of aluminium and iron on page 47 of the student’s book.
Corrosion
Ask the students: what happens to a piece of iron if left in the garden for a long time?
Discuss corrosion with some every day examples. Explain that when a metal is attacked by air, water or
other substances in its surroundings, the metal is said to ‘corrode’. In general, the more reactive a metal
is, the more readily it corrodes.
Explain that iron and steel are among the most widely used materials in our society. This is because iron is
one of the easiest and cheapest metals to extract from its ore. However, when iron and steel are exposed
to the damp weather over long periods of time, they rust. During rusting, iron combines with oxygen to
form a red powder called iron oxide. The rusting of iron and steel causes a great deal of damage, so it is
very important to try to prevent rusting.
Corrosion of other metals
Ask the students: what kind of materials corrode?
Explain that metals such as the reactive alkali metals corrode so easily in air that they are kept under
oil for safety. Other metals are very resistant to corrosion—gold and silver are good examples. Not all
corrosion of metals causes problems. Copper reacts with oxygen and carbon dioxide in the atmosphere
and becomes coated with a bluish-green encrustation called verdigris.
This protects the copper underneath from further attack. Aluminium reacts with oxygen to form a thin
layer of aluminium oxide. This layer protects the aluminium from further corrosion in the same way. The
aluminium layer is made thicker if the aluminium is to be used for window frames. This is carried out by
electrolysis and is called anodizing.
Answers
Patterns of reactivity: p 42
1.
Metals conduct electricity. They conduct heat. They are strong. They can be shaped. They make a
noise when hit.
2.
Since the Bronze Age, about 4000 years ago.
3.
Metals are used in making aircraft, ships, cooking utensils, jewellery, statues, pylons, electric cables,
etc.
4.
cutlery, wires, cooking pots, furniture, etc.
How do metals react: p 43
1.
sodium
2.
magnesium and calcium
3.
calcium, sodium, and potassium
4.
An unreactive metal does not react with either water or acid. For example: gold
5.
They do not tarnish.
6.
Metals react most easily with acid, such as aluminium, zinc, iron, tin, and lead. These metals do not
react with air or water readily. Metals that react with water often react very violently with acids, e.g.
sodium, potassium, and calcium.
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The reactivity series: p 44
1.
Metals can be arranged in a sort of league table according to the way they react. This league table is
called the reactivity series.
2.
Potassium is at the top of the reactivity series because it burns in air, reacts fastest with water, and
violently with acid.
3.
K (potassium), Na (sodium), Ca (calcium), Mg (magnesium), Fe (iron), Cu (copper), Ag (silver)
4.
a)
Sodium reacts violently giving off hydrogen gas.
b)
Magnesium reacts violently with steam.
c)
Iron reacts very slowly forming a reddish coating (rust) on the surface.
d)
Gold is not affected by a weak acid.
Displacement reactions: p 45
1.
2.
a)
A more reactive metal such as iron (higher up in the reactivity series) takes the place of a less
reactive metal such as copper (lower down in the series) during a chemical compound.
b)
In case of zinc, a similar reaction would have taken place where zinc ions would have replaced
the copper ions to form zinc sulphate. No reaction would take place with silver because it is lower
down in the reactivity series.
a)
The experiment shows that the metal X is higher than copper and lower than iron in the reactivity
series. This means that metal X could either be lead or iron.
b)
In order to find out the identity of metal X, the student should place separate samples of the
metal in iron sulphate and lead nitrate solutions simultaneously.
If the metal shows no reaction with iron sulphate, but reacts with lead nitrate, then metal X is
iron. This can be defined as a displacement reaction where a metal higher up in the reactivity
series replaces a metal lower in the series from its solution.
In case the metal does not react with any of the solutions, metal X is lead.
Metal from the Earth: p 46
1.
silver
2.
a)
Compounds of metals found in rocks are called ores.
b)
This is because these metals are reactive and at some time in the past they have reacted with
elements like oxygen and sulphur to form compounds like oxides and sulphides. This most likely
happened in parts of the Earth where temperatures were very high.
3.
a)
oxygen
b) sulphur
4.
a)
iron
b) aluminium
5.
a)
Recycling means to collect and reuse materials.
b)
All natural resources are not going to last forever. Minerals such as bauxite (aluminium ore) may
run out in our lifetimes. Oil, which is used as a raw material for the manufacture of many plastics,
is running out now.
c) oxygen
Extracting metals from their ores: p 47
52
1.
First the metal is separated from the rock and other waste material. Next, the metal has to be extracted
from the metal compound.
2.
Metals lower in the reactivity series form less stable compounds, so they can be separated from their
ores more easily.
3.
a)
Impurities are removed from the bauxite leaving pure aluminium oxide or alumina. The alumina
is melted, and then an electric current is passed through the hot liquid; pure aluminium is
produced.
b)
Copper could be extracted by the same method, as it is high in the reactivity series it forms stable
compounds.
4.
Carbon is added to iron oxide in a blast furnace so that oxygen is removed from it by forming carbon
dioxide, leaving behind pure iron.
5.
Aluminium is high in the reactivity series and forms stable compounds which need a lot of energy to
split them. Iron being a metal lower in the reactivity series forms less stable compounds and can be
separated from its ore more easily.
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Corrosion: p 48
1.
A metal corrodes whenever a chemical, such as water, air or acid attacks its surface.
2.
Metals high up in the reactivity series cannot be used to make things because they are quickly
corroded by air and water.
3.
a)
Corrosion can weaken the iron or steel and make it dangerous to use.
b)
It becomes rusty and does not move easily.
a)
by painting it
b)
by electroplating it with chromium
c)
by oiling it
4.
5.
Sacrificial protection is a process in which plates of a more reactive metal is put onto another less
reactive metal to protect it from corroding.
Beating corrosion using alloys: p 49
1.
An alloy is a mixture of two or more metals.
2.
Alloys are usually made by melting metals together and then allowing the molten mixture to cool and
harden.
3.
a)
Steel is stronger and more rust-resistant than iron.
b)
Bronze is stronger than copper.
c)
It is harder and stronger than aluminium.
a)
Monel is strong and unaffected by sea water.
b)
Solder melts at low temperatures, and then sets hard.
a)
solder
4.
5.
b) stainless steel
c) bronze
Test yourself: p 50–51
1.
2.
3.
4.
5.
a)
Silver is deposited at the cathode.
b)
Hydrogen gas is given off.
c)
No reaction takes place.
d)
A violent reaction takes place.
a)
In the tube containing water and air.
b)
Oxygen combines with iron to form iron oxide which is rust.
c)
iron + water ‡ iron oxide + hydrogen
d)
It weakens the iron.
e)
By oiling and by painting.
(A is copper, B is lead, C is gold, D is zinc)
a)
Metal D is zinc which is the most reactive because it is higher up in the reactivity series as
compared to the other metals in the table.
b)
It will form lead chloride and hydrogen gas.
c)
It will displace copper and form zinc sulphate.
a)
i) bauxite ii) haematite iii) copper pyrites
b)
It is more expensive to extract.
c)
It is corrosion resistant and it is light in weight.
d)
Because aluminium is expensive to extract.
a)
for extracting iron
b)
iron oxide, coke, and limestone
c)
waste gases
d)
hot air
e)
molten iron
f)
Iron oxide is first separated from impurities in the haematite. It is then put into a blast furnace
along with carbon, where it is heated strongly. Oxygen is removed from the iron oxide leaving
pure iron. This process is known as smelting.
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6.
a)
It is corrosion resistant.
b)
Tin is used because it is non-toxic and less reactive than the iron in the steel.
c)
The layer of steel or iron would be exposed, which is toxic.
Workbook 3, chapter 5
1.
a)
i) potassium
ii) gold
b)
Gold is an unreactive metal so it can be dug out as a pure metal, but iron is very reactive so it
can only be found as a compound in iron ore.
c)
They are shiny metals which do not react with any other element easily.
d)
i)
No
ii)
Aluminium is the most abundant metal in the Earth’s crust, but it is found in the form of an
ore called bauxite.
2.
U, P, O
3.
a)
Aluminium is a metal which is high up in the reactivity series and it forms stable compounds.
These compounds need a lot of energy to split them.
b)
i) the positive electrode
ii) the negative electrode
c)
i) graphite
ii) graphite
d)
Molten aluminium is denser than molten aluminium oxide.
e)
It is very expensive to extract.
f)
1.
Its good conductivity of electricity makes it useful for making cables and wires in the electric
industry.
2.
It is a light weight metal with low density. It is used to make light objects that need to last
for a long time, for example, aeroplanes.
4.
5.
a)
oxygen
b)
It is put into a blast furnace along with carbon and the mixture is heated strongly. Oxygen is
removed from the iron oxide leaving behind pure iron.
c)
i)
Coke (carbon) reacts with oxygen in the air to produce carbon dioxide.
ii)
To produce energy for the process to continue.
d)
1900°C
e)
Carbon dioxide + iron
a)
Test tube 1—no reaction
Test tube 2—no reaction
Test tube 3—the nail is rusty
6.
b)
The oxidation of iron can only take place in the air with moisture.
c)
iron gate
painting
steel dustbin
galvanizing
kitchen tap
electroplating
ship’s hull
sacrificial protection
A more reactive metal can protect a less reactive metal in a process called sacrificial protection.
Plates of reactive metals such as magnesium are ‘sacrificed’ to save such metals as iron or steel from
corroding. This method is used for protecting ship hulls. Because the hull is always under water, it
cannot be painted regularly.
Underground gas and water pipes can be protected in the same way.
7.
54
a)
An alloy is a mixture of two or more metals.
b)
Bronze is an alloy of copper and tin. Tin is stronger than copper, so a bronze model is harder to
deform.
c)
Bronze is used to make statues.
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Projects
1.
To investigate the conditions which cause rusting.
Place four clean iron nails into each of the five test tubes labelled A to E, and prepare them in the
following way:
Tube A:
leave the test tube open
Tube B:
fill half of the tube with distilled water
From here it gets confusing
Tube C:
fill half of the tube with boiled distilled water. Pour some oil such that it forms a thin layer
on top of the water. Close the mouth of the test tube with a rubber bung.
Tube D:
dissolve some salt in water and add this to the tube D
Tube E:
put some solid calcium chloride (removes moisture) into tube E, and close its mouth with
a rubber bung.
Leave the test tubes in the rack for a week.
Record your results in the table below.
Test tube
Appearance after two days
Appearance after one week
A
B
C
D
E
In which test tube did the nails rust most?
In which test tube did the nails rust least?
Under what conditions do iron and steel rust most?
Ask the students: can you think of some ways in which we can prevent metals from rusting and
corrosion?
2.
Write a list of the methods of preventing corrosion on the board and ask the students to find out
about each method and write them down. They can use reference books in the library or surf the
Internet for research.
paint
grease
plastic coating
tin plating
chromium plating
sacrificial protection
galvanizing
Multiple Choice Questions
1.
Which one of the following metal does not react with water or steam?
A sodium
2.
A gold
3.
B potassium
C magnesium
D gold
Which one of the following metals does not react with acid?
B sodium
C potassium
D calcium
Which one of the following metals burn easily in oxygen?
A silver
B gold
C magnesium
D iron
4. Which reacts with hydrochloric acid to give hydrogen?
A ammonia
5.
6.
B iron
C silver
D sodium hydroxide
What is the correct order of the metals in the reactivity series?
A copper, zinc, sodium
B zinc, sodium, copper
C sodium, copper, zinc
D sodium, zinc, copper
A displacement reaction takes place only when the metal that is put into the solution is
reactivity series than the metal in the solution.
A higher
B lower
C at the same level
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7.
Which substance is not an essential raw material in the extraction of iron in a blast furnace?
A air
8.
B coke
D sand
Which substance removes impurities from iron ore in the blast furnace?
A carbon
9.
C limestone
B limestone
C sand
D slag
Gold and platinum may be found uncombined in the Earth’s crust because
A they are rare elements
B they are difficult to obtain
C they do not form compounds easily
D they do not melt easily
10. An alloy is a mixture of two or more
A gases
B metals
C non-metals
Answers
1.
D
6. A
56
2. A
3. C
4. B
5. D
7.
8. B
9. C
10. B
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D liquids
C
6
er
hapt
Gravity and space
Unit flow chart
Weight in space
Early ideas about the solar system
Keeping the planets in orbit
Satellites in orbit
Information from satellites
Aims and learning objectives
•
To learn that the gravitational pull between bodies depends on their mass and the distance between
them
•
To describe how weight is different on different planets
•
To explain that the Sun’s gravitational force keeps the planets in orbit
•
To show how artificial satellites are used to observe the Earth and provide information about the solar
system and the universe
Background information
Everyone knows that an object falls to the ground when it is dropped. This downward motion is the result
of the force of gravity, or gravitational force.
It was Sir Isaac Newton who came to the conclusion that a gravitational force exists between bodies. Not
only are objects attracted towards the centre of the Earth, but they also attract each other.
Newton came up with a law of gravitation, which says: Any two particles of matter attract one another with
a force which is proportional to the product of their masses (mass1 x mass2) and inversely proportional to
the square of their distance apart.
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This means, in simple terms, that the pull of gravity between two objects depends upon the mass of
the objects and the distance between them. Every object in the universe attracts other objects. It is
gravitational force which keeps the Moon in orbit around the Earth and the planets of the solar system in
their orbits around the Sun.
Unit introduction
Centripetal force
Additional activity 1
Tie a rubber bung to the end of a string and swing it over your head in a circle.
Ask the students: what keeps the object moving round and round?
Explain that to keep any object moving in a circle there must be a force acting on it directed towards
the centre. This force is called centripetal force.
Ask the students: what keeps the planets of the solar system moving very quickly through space?
Explain that centripetal force keeps them moving because there is nothing to slow them down. Centripetal
force is needed to produce the continuous change of direction which occurs in an orbit. It is provided by
the gravitational attraction between the planets and the Sun.
Additional activity 2
Attach a suitable object such as a rubber bung, to the end of a piece of a string one metre long.
Stand well clear of any obstruction and swing the object round and round.
The pull of the string is providing the centripetal force.
What happens to this force if you:
•
increase the speed of rotation?
•
alter the length of the string?
•
change the mass of the object?
Teaching procedure
Ask the students: how much do you weigh? What is mass? Discuss the difference between mass and
weight.
Explain that weight is another name for the gravitational force from the Earth. As weight is a force it is
measured in newtons (N). On Earth, each kilogram (kg) of matter is equal to 10 newtons.
People often use the word ‘weight’ when they really mean ‘mass’. If you have a mass of 50 kilograms, you
weigh 500 newtons.
How to lose weight quickly
Go to the Moon or even better, go deep into space, far away from all the planets.
As different planets have different masses and sizes, your weight would vary from one place in the
Universe to another.
Discuss the difference between mass and weight of the same object in different places:
Place
Mass
Weight
Earth
50kg
500N
Moon
50kg
80N
Jupiter
50kg
2700N
Deep in space
50kg
zero
50kg
100 million, million N
Near a black hole
(a collapsed star)
Ask the students: why is there a difference in the mass and weight?
Explain that travelling around space is not going to get rid of the kilograms. Weight may vary, but mass
stays the same. On the Moon for example, the gravitational pull is much less than on Earth. But the
amount of matter in something is just the same. And it is just as difficult to speed up or slow down.
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Additional activity 3
Aliens landed on several planets, including Earth. Here is some information about them:
Alien
Mass in kg
Weight in N
A
40
80
B
20
200
C
10
200
D
20
40
1.
Which alien landed on Earth?
2.
Which two aliens landed on the same planet?
3.
The aliens have to jump from their spacecraft when they land. Which alien will fall with the greatest
acceleration?
4.
If all the aliens came to Earth, which would weigh least?
Discuss the early ideas about the solar system with the students. Which scientist do you think is closest to
the present day theories about the universe and the solar system? How did Galileo show that the Earth is
not the centre of the universe? Discuss.
Satellites
Ask the students: what is a satellite?
Explain that on a starry night you can sometimes see a star that is moving slowly.
Ask the students: what could it be?
Explain that the Moon is the Earth’s natural satellite, but there are plenty of artificial satellites too. Like
the Moon they are held in orbit around the Earth by gravitational force. Because their orbits are smaller,
satellites close to the Earth take less time to go round it then those further away. At a height of 160 km,
one orbit takes about one hour and a half. Some satellites are just discarded rockets from space launches.
Others are put into orbit for special purposes.
Weather satellites
‘Tiros’, the first of many civilian weather satellites, was launched in 1960. Some weather satellites are
positioned far above the Earth’s surface to give an overall view of cloud formations and movements.
Others orbit closer to the Earth to give more detailed information on clouds and temperatures.
Land satellites
‘Landsat’ is one of many such satellites. It is in close orbit round the Earth and has an orbit time of 1¾
hours. As it passes overhead, Landsat views a strip of the Earth’s surface. The information collected is
used to study such things as water pollution, the effect of industry on the environment, and to distinguish
different types of crops. Landsat images are also used for making maps.
Communication satellites
They are used to transmit telephone calls, television broadcasts, and other electronic information from one
country to another. Global positioning satellites transmit data so that ships and aircraft can locate their
position to within 100 metres. Both are in geostationary orbit.
You can see artificial satellites as star-like points of light travelling quite slowly across the background of
the stars.
They are lit up by the Sun’s light. The best time to look for satellites is just after dark in the evening or
just before sunrise, though in summer you can see them all night. During one half hour you might see
three or four satellites. A satellite often travels across the sky for a few minutes before slowly fading in
brightness as it passes into the Earth’s shadow.
Answers
Gravity and space: p 52
1.
Gravitational force pulls all objects towards the centre of the Earth.
2.
Newton made the discovery about gravity after seeing an apple fall from a tree.
3.
The size of the gravitational force depends on masses of the two objects attracting each other; the
bigger the masses the greater the forces due to gravity.
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4.
The size of the gravitational force depends on the distance between the two objects. As the distance
increases, the force due to gravity decreases.
5.
There is a gravitational force between them because they are so big and heavy, and the distance
between them is small.
Weight in space: p 53
1.
a)
The weight of an object is the force of gravity pulling down on it; the greater the force of gravity
the greater the weight.
b)
Weight is measured in newtons (N).
2.
10N
3.
a)
The gravitational field strength of the Earth is called ‘g’.
b)
10N/kg
4.
4kg x 10N = 40N/kg.
5.
Venus has a smaller mass than Earth.
6.
1/6 of 600N = 100N
Early ideas about the solar system: p 54–55
1.
Stonehenge was a complex astronomical computer which was built about 4000 years ago. It could be
used to predict when eclipses could occur.
2.
The shadow would be a straight line.
3.
Thales of Melitus explained that the Earth was a flat disc floating on an infinite ocean. He explained
earthquakes by imagining that earthquakes occurred when the Earth was rocked by waves.
4.
Aristarchus was known as the Greek Copernicus because he was the first recorded person to suggest
that the Sun, not the Earth, was at the centre of the known universe.
5.
Copernicus had problems with the Church because he believed that the sun and not the Earth was
the centre of the Universe. The Church could not believe that God had arranged everything in such a
way that the Earth was not the centre of the Universe.
6.
Galileo saw, with his telescope, four moons orbiting the round Jupiter. By showing that there were
objects which did not orbit the Earth, he showed that the Earth did not have to be at the centre of
everything.
Keeping the planets in orbit: p 56
1.
The planets are held in orbit by the Sun’s gravitational pull.
2.
They keep moving at very high speeds through space because there is very little friction to slow them
down.
3.
a)
A comet is a huge lump of rock and ice that also orbits the Sun.
b)
The orbit of a comet is elliptical, whereas the Earth’s orbit is almost circular.
a)
The head of a comet is a lump of ice several kilometres across. When this is heated by the Sun,
dust and gas stream off into space forming a huge tail millions of kilometres long.
b)
The tail of a comet is visible because it reflects sunlight.
4.
Satellites in orbit: p 57–58
1.
60
a)
Any object in orbit around a more massive one is called a satellite.
b)
The moon is a natural satellite of the Earth.
2.
The curved path, taken by a satellite travelling at a very high speed, matches the curve of the Earth.
Since there is no air resistance to slow it down, it will keep its speed and stay in orbit.
3.
It is the pull of gravity towards the centre of the Earth which keeps them in orbit.
4.
A satellite must be above the Earth’s atmosphere to avoid being pulled down to the Earth by
gravitational force.
5.
A polar orbit of a satellite passes over the North and South Poles. As the Earth turns beneath them
they can scan the whole of its surface. A geostationary orbit of a satellite remains at the same speed
as the earth rotates.
6.
As a geostationary satellite orbits the Earth at the same speed as the Earth rotates, so they stay in
the same relative position in the sky.
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Information from satellites: p 59
1.
Weather monitoring satellites, navigation satellites, communication satellites and research satellites.
2.
Communication satellites are normally put into a geostationary orbit. They rotate at the same speed
as the Earth rotates so stay at the same relative position in the sky.
3.
Sat Nav systems are navigation satellites. They send out radio signals which can be picked up by
motor vehicles to find their position.
4.
The Hubble Space Telescope uses radio signals to send pictures to the Earth which are not disturbed
by the atmosphere or the Earth’s gravity.
5.
Weather monitoring satellites study cloud formation above the Earth. This helps in weather
forecasting.
i)
ii)
M
iii)
pull of
gravity
pull of
gravity
Earth
pull of
gravity
Earth
Earth
Test yourself: p 60–61
1.
2.
3.
a) and b)
c)
Gravitational force pulls all objects towards the centre of the Earth.
a)
almost three times greater
b)
i) 200kg
c)
They will weigh one-third less than their weight on Earth, so they will not be able to walk properly.
Their strides will be longer.
a)
Gravitational force depends on the masses of the bodies and the distance between them.
b)
Copernicus suggested that the Sun, and not the Earth was at the centre of the universe. The
Church at that time could not believe that God had arranged things so that the Earth was not in
the centre. ‘Everything’, they said, ‘must revolve around the Earth’.
c)
i)
Galileo
ii)
around Jupiter
d)
4.
ii) 66kg
iii) 198N
We can get information about the universe from the pictures and radio signals sent by these
satellites and telescopes.
a)
Sun
E
H
b)
A comet is a huge lump of rock and ice that orbits the Sun.
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5.
c)
In the head of the comet is an icy lump several kilometres across. When this is heated by the
Sun, dust and gas stream off it into space forming a huge tail millions of kilometres long. This
tail is visible because it reflects sunlight.
d)
i)
The Earth’s orbit is almost circular whereas the orbit of Hailey’s comet is elliptical.
ii)
The gravitational pull of the Sun is the centripetal force which keeps the Earth on its circular
path and prevents it flying out into space. Hailey’s comet has an elliptical orbit because it
has less speed when furthest from the Sun. This is also when the Sun’s gravitational pull on
it is the weakest. As the comet moves closer to the Sun, it speeds up.
e)
Hailey’s comet can be seen regularly because it has an elliptical orbit.
a)
B
b)
i)
c)
6.
B
ii)
It is pulled by a greater gravitational force than A because it is closer to the Earth.
i)
A
ii)
A satellite is further away from the Earth therefore its gravitational field strength is smaller
than that on B.
d)
It means that A orbits the Earth at the same speed as the Earth rotates, so it stays in the same
relative position in the sky.
e)
Communication satellites are put into a geostationary orbit so that they stay in the same relative
position in the sky. On the ground, dish aerials sending and receiving signals can point in a fixed
position.
a)
12
b)
Low polar orbits pass over the North and South Poles of the Earth, so they can scan the whole
of its surface. They can study the cloud formation above the Earth. This helps in weather
forecasting.
c)
navigation satellite
d)
A low polar orbit would be useless for a communications satellite as the Earth’s gravitational field
would disturb the signals sent and received by them.
e)
TV programmes and weather forecasts.
Workbook 3, chapter 6
1.
a)
Earth’s pull in N
50
40
30
20
10
0
1
2
3
4
5
mass in kg
62
b)
The bigger the masses the greater the forces due to gravity.
c)
10N
d)
As the distance increases, the force due to gravity decreases.
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2.
a)
It is 8.4N/kg greater.
b)
Mass on Earth
Weight on Earth
Mass on moon
Weight on moon
2.0kg
2×10 = 20N
2kg
2×1.6 = 3.2N
1.0kg
1×10 = 10N
1kg
1×1.6 = 1.6N
10 .0kg
10×10 = 100N
10kg
10×1.6 = 16N
0.1kg
0.1×10 = 1N
0.1kg
0.1×1.6 = 0.16N
100.0kg
100×10 = 1000N
100kg
100×1.6 = 160N
c)
The gravitational field strength of the Earth is greater than that on the moon.
d)
g on Earth
= 10N/kg
g on Jupiter
= 2.6 x 10
= 26N/kg
Mass of object
= 2kg
Weight of object on Earth = 2 x 10 = 20N
Weight of object on Jupiter = 2 x 26 = 52N
3.
The planets of the solar system are in orbit round the Sun. They are held in orbit by the Sun’s
gravitational pull. They keep moving at very high speeds through space because there is very little
friction to slow them down.
The orbits of the planets are shaped like ellipses. The Earth’s orbit is almost circular, with the Sun
at the centre. The gravitational pull of the Sun is the centripetal force which holds the Earth on its
circular path and prevents it from flying out into space.
4.
5.
a)
Sir Isaac Newton
b)
Thales of Miletus
c)
Galileo Galilei
d)
Galileo Galilei
e)
Aristarchus
f)
Nicolas Copernicus
a)
A comet is a huge lump of rock and ice that orbits the Sun.
b) and c)
comet
W
Sun
Earth
S
d)
i) W
e)
When the head of a comet is heated by the Sun, dust and gas stream off into space forming a
huge tail millions of kilometres long.
ii) S
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6.
7.
f)
The tail is visible because it reflects sunlight.
a)
D
d)
This is so because the Moon has lesser gravitational force than the Earth.
a)
i)
The curve of its fall matches that of the Earth.
ii)
It falls to the Earth.
i)
A polar orbit is an orbit of a satellite that passes over the North and South poles.
ii)
As the Earth turns beneath them, they can scan the whole of its surface.
i)
They orbit at the same speed as the Earth rotates, so they stay in the same relative position
in the sky.
ii)
Due to their geostationary orbit, satellites remain in the same relative position in the sky
that is why dish aerials sending and receiving signals can point in a fixed direction.
b)
c)
b) C
c) A
Project
1.
Discuss the different types of satellites that are sent into space. If possible take the students to
a planetarium (if there is one in your city) and show them the pictures about space, planets, and
satellites. Ask them to collect as much information as they can from books, magazines and the net.
2.
Make a list of things artificial satellites are used for.
Try to find about the various satellites which are used for space research.
(The ‘Hubble’ telescope is just one example).
Multiple Choice Questions
1.
Which one of the following scientists came to the conclusion that gravitational force exists between
all bodies?
A Newton
2.
B Galileo
C Hooke
The weight of a body is the force of
A pressure
3.
B gravity
pulling on it.
C friction
A mass and gravity
B mass and length
C mass and distance
D mass and pressure
How much would a bag of sugar with a mass of 1 kg weigh on the moon?
A 1.7N
5.
B 3.8N
C 9N
D 10N
Which Greek philosopher is known as the ‘Greek Copernicus’?
A Thales of Melitus
6.
B Aristarchus
C Copernicus
D Galileo
The planets of the solar system are held in orbit by
7.
A the Sun’s gravitational pull
B the attraction between the planets
C the force of the Earth’s gravity
D the force of attraction of the moon
Huge lumps of rock and ice that orbit the Sun are called
A meteors
8.
B meteorites
C comets
D planets
Satellites that survey the Earth are put in a
9.
A high polar orbit
B low polar orbit
C geostationary orbit
D research orbit
Satellites that pass on telephone and TV signals from one place to another are called
A relay satellites
B communication satellites
C travelling satellites
D research satellites
10.
satellites help in weather forecasting
A communication satellites
B navigation satellites
C weather monitoring satellites
D research satellites
Answers
A
6. A
64
D acceleration
What two things affect the gravitational attraction between objects?
4.
1.
D Pascal
2. B
3. C
4. D
5. B
7.
8. B
9. B
10. C
C
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Plants and
photosynthesis
Unit flow chart
The chemistry of photosynthesis
The products of photosynthesis
What happens to the glucose?
Plant needs
Photosynthesis and respiration
Aims and learning objectives
•
To understand that photosynthesis is the source of biomass
•
To identify the raw materials for photosynthesis
•
To identify light as a source of energy for photosynthesis
•
To describe how leaves are adapted for photosynthesis and how roots are adapted to take in water
•
To understand the chemistry of photosynthesis
•
To appreciate the importance of photosynthesis to humans and other animals
•
To explain the difference between photosynthesis and respiration
Background information
Photosynthesis: what happens inside the cells?
Photosynthesis is not one simple, chemical reaction; rather it is a series of complicated reactions. Each
reaction is controlled by special chemicals called enzymes.
We can represent what happens during photosynthesis by one equation:
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carbon dioxide + water ‡ glucose + oxygen
(energy from sun)
The presence of sunlight and chlorophyll is very important for the above reaction to take place in a plant.
Unit introduction
Ask the students: what is the food of a plant? How do plants eat? What is photosynthesis? Where does it
take place? How can we know that a plant is making its food? Write the equation for photosynthesis on the
board and discuss it.
Teaching procedure
Ask the students: what is the product of photosynthesis?
Testing a leaf for starch
Perform the starch test on a leaf and show the students the presence of starch.
Why do we test a leaf for starch to see if photosynthesis has been taking place in it or not?
Explain that usually the glucose made by photosynthesis is converted to starch. This is then stored for a
short time in the leaf until it is needed.
Ask the students: what are some of the things necessary for photosynthesis to take place?
Explain that the starch test is important because we can test the leaves of plants which have been kept in
different conditions. A leaf which has been growing in the dark will not contain starch. Neither will a leaf
that has had its supply of carbon dioxide cut off. Variegated leaves only contain starch in the areas where
there is chlorophyll.
Plants need water
Ask the students: what happens to a plant if we do not water it for a long time?
Explain that it wilts because all living things need water for the chemical reactions that take place inside
them, to transport materials around the body and to carry away waste. In addition, plants use water to
carry minerals from the soil into their roots.
Ask the students: how does water enter a plant?
Explain that water enters the roots by a process called osmosis. Osmosis is the diffusion of water from a
weak to a strong solution through a selectively permeable membrane.
Draw a section of a root hair and explain that root hairs take in water by osmosis because their cell
contents are stronger than the surrounding soil and because their cell membranes are selectively
permeable.
As root hair cells take in more and more water by osmosis their cell contents become weaker than the
cells next to them. So, water moves across into cells lying further inside the root.
If water continually enters a root system a pressure is built up. This root pressure helps move water
through the plant, particularly in spring when plants begin to grow again.
Plants need minerals
Ask the students: do plants need minerals? Why?
Explain that the element nitrogen is essential for life because it helps to form protein, the material of
which all living things are made.
Ask the students: how do plants get their nitrogen supply?
Explain that the air contains approximately 80% nitrogen. Unfortunately animals and plants cannot use
nitrogen gas directly from the air. Plants must have their nitrogen combined with oxygen in the form of
nitrates which they absorb from the soil. Animals get theirs by eating plants. In this way nitrogen passes
along food chains. Eventually nitrogen passes back into the air.
The circulation of nitrogen compounds in the environment is called the nitrogen cycle.
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Atmospheric
Nitrogen
Lightening
produces oxides
of nitrogen
Nitrogen fixing bacteria
in humus & root nodules
of leguminous plants
Taken up by
plant roots
Eaten by
herbivores, in
turn eaten by
carnivores
Denitrifying bacteria
breakdown nitrates,
release oxygen &
nitrogen into the air
Dead plants
& animals,
urine & faeces
release nitrates
in soil
Soil nitrates
The nitrogen cycle
Minerals from the soil
Ask the students: how do plants get their supply of minerals from the soil?
Explain that plants need nitrogen and other elements for normal, healthy growth. Mineral salts from the
soil enter the roots of plants in the form of ions in solution. Some ions may enter by simple diffusion but
most get into the cells of the root by a process called active transport. Active transport uses energy to
move ions into the root cells. It means that plants can take ions into their cells, when there are more ions
in the cells than in the soil.
Additional activity 1
Make a chart
Mineral elements needed by plants
Element
Ions in the soil
What it is used for
nitrogen
nitrate ions
a vital part of protein for growth
calcium
calcium ions
important for making cell walls
iron
iron ions
for making chlorophyll
magnesium
magnesium ions
for making chlorophyll
phosphorus
phosphate ions
a part of genes, chromosomes, cell membranes
potassium
potassium ions
involved in enzyme activity
sulphur
sulphate ions
used in important proteins
There are other elements that plants require but in very small quantities. These trace elements include
manganese, zinc, and copper.
The carbon cycle
Ask the students: why do all living things need the element carbon?
Explain that all living things contain the element carbon. It is the basic element of which all living
things are made. Plants need carbon as a raw material for making their food. Carbon circulates from the
environment into living things and then back again. This is known as the carbon cycle.
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Draw the carbon cycle on the board and discuss the circulation of carbon between living and non-living
things.
Explain that when we burn fossil fuels, carbon dioxide is given off. At the same time, lots of the world’s
jungles and forests are being cut down. This means that there are few plants to photosynthesize and
produce oxygen. These two activities may be upsetting the balance of the gases in our environment and so
scientists must continually monitor what is happening in our atmosphere.
Atmospheric
carbon dioxide
Animal & plant
respiration
Photosynthesis
Food for animals
Green Plants
Combustion
Fossil fuels
The carbon cycle
Comparison between photosynthesis and respiration
Photosynthesis
Respiration
Kind of process
Building up
Breaking down
Raw materials
Carbon dioxide and water
Glucose and oxygen
Energy changes
Energy required
Energy released
End-products
Glucose and oxygen
Carbon dioxide and water
Time of occurrence
During daytime or in the presence of light
All the time
Discuss the above comparison in class. Also discuss the gaseous exchange between green plants and
the atmosphere that takes place during the day and at night. Discuss the balance of oxygen and carbon
dioxide in the atmosphere.
Discuss the effects of the increasing amount of carbon dioxide in the atmosphere and global warming in
relation to it.
Answers
Plants and photosynthesis: p 62
1.
Plants are part of our food chain.
2.
Photosynthesis takes place in the leaves of green plants.
3.
Energy for photosynthesis comes from the Sun.
4.
a)
chlorophyll
b)
Chlorophyll is contained in chloroplasts inside plant cells.
5.
Leaves are well adapted for the function they perform. Their broad, flat, thin shape provides a large
surface area, ideal for absorption of carbon dioxide and sunlight.
The chemistry of photosynthesis: p 63
68
1.
carbon dioxide + water – sunlight absorbed by chlorophyll ‡ glucose + oxygen
2.
From sunlight
3.
a)
Carbon dioxide and water
b)
Carbon dioxide enters the leaf through stomata by diffusion. Water is carried to the leaf in the
xylem tubes from the stem.
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4.
glucose
5.
a)
Oxygen diffuses into the air through stomata.
b)
It is this oxygen that all living things use for respiration.
6.
The leaves of the Potomageton natans float on the surface of the water so its stomata are on the
upper surface as the under surface of the leaf is submerged in water.
Photosynthesis: the starch test: p 64
1.
The iodine turned from brown to blue-black at the end of the test. It does so only in the presence of
starch. Therefore, the test shows that the leaf had been photosynthesizing.
2.
a)
brown
b)
blue-black
a)
To soften it.
b)
Alcohol removes the green colour.
c)
To soften it.
a)
After heating the leaf in alcohol to remove the green colour the flame must be put out.
b)
Alcohol Burns
3.
4.
Photosynthesis: testing the equation: p 65
1.
carbon dioxide
2.
A variegated leaf has green and white or yellow parts. There is no chlorophyll in the white parts.
3.
Starch will be present only in the uncovered part.
4.
The leaf should remain attached to the plant otherwise it will not get water which is essential for
photosynthesis to go on.
5.
It bursts into flame.
What happens to the glucose: p 66
1.
a)
Respiration takes place inside every living plant cell.
b)
Respiration takes place all the time.
2.
Glucose is changed into insoluble starch or oil and stored in the roots, stems, seeds, and fruits.
3.
Cellulose is used to make new cell walls.
4.
a)
Nitrogen from the soil is joined up with glucose to make protein.
b)
Plants need protein for growth.
5.
Magnesium is an element which is joined with glucose to make chlorophyll.
Plants and water: p 67
1.
a)
Roots help to absorb water for the plant.
b)
The surface area of roots is increased by many thousands of root hair cells which have thin
walls.
2.
A thin cell membrane makes it easy for water and minerals to pass through. It also helps the cells to
absorb oxygen easily from air in the spaces between the soil particles.
3.
a)
Water enters the root hair cells because the water concentration outside is stronger than that
inside the cells.
b)
Running through a plant is a miniature pipeline of tubes called xylem, which carries water to the
rest of the plant.
a)
Root cells get their oxygen from the air in the spaces between the soil particles.
b)
Roots need oxygen for respiration.
4.
Plants need minerals: p 68
1.
Plants need minerals for normal, healthy growth.
2.
Some minerals come from rocks, dissolved in rainwater. Others come from the faeces and urine of
animals, and the dead bodies of plants and animals as they decay. Farmers add artificial fertilizers to
the soil which contain all the minerals that crop plants need.
3.
Leaching is the washing away of soil minerals when they dissolve in rainwater running through the
soil.
4.
In cultivated soils, removal of minerals takes place by uptake of minerals by plants and by leaching.
So fertilizers have to be added to improve the fertility of the soil.
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5.
Mineral salts get into the roots of plants in solution. Some dissolve in the water in the soil and then
enter the root hair cells in water. Most minerals, however, are moved into the plant root cells using
energy.
Photosynthesis and respiration: p 69
1.
a)
photosynthesis
carbon dioxide + water ‡ glucose + oxygen
(energy needed)
b)
respiration
glucose + oxygen ‡ carbon dioxide + water
(energy released)
2.
Photosynthesis is the opposite of respiration.
photosynthesis
respiration
building up process
breaking down process
energy used
energy produced
glucose is produced
glucose is used
oxygen is produced
oxygen is needed
water is used
water is produced
3.
Oxygen is used for: burning, breathing, and for photosynthesis.
4.
Fewer trees were cut down and less fossil fuels were burnt.
5.
Trees use carbon dioxide for photosynthesis and release oxygen, thereby maintain the level of carbon
dioxide and oxygen in the atmosphere. Cutting down trees would simply increase the amount of
carbon dioxide in the atmosphere. It would also reduce the amount of oxygen in the atmosphere.
Test yourself: p 70–71
1.
a)
A water
B carbon dioxide
b)
D oxygen
E glucose
c)
sunlight
d)
carbon dioxide + water ‡ glucose and oxygen
e)
By testing it for starch.
a)
Put a leaf in boiling water for two minutes to soften it.
(energy from sun)
2.
Put out the Bunsen flame.
Heat the leaf in alcohol to take away the green colour.
Soften the leaf in water.
Add iodine to the leaf.
3.
4.
5.
70
b)
If the leaf turns a blue-black colour, it has starch in it.
c)
The starch has been made in the leaf during photosynthesis.
a)
A culture solution is a solution of mineral salts that are necessary for plant growth.
b)
Air is pumped into the solution so that the roots can respire.
c)
It is covered with a black card so that light does not enter the solution.
d)
It can grow without soil as the culture solution contains all the necessary minerals for plant
growth.
a)
It uses the stored glucose for growth, respiration, and for storage when the leaves fall off.
b)
Cellulose is used for making cell walls.
c)
i) nitrogen
d)
They contain stored sugar.
a)
From the soil.
b)
From the root hairs which have very thin cell walls.
c)
They have thousands of tiny root hairs which have very thin walls which can absorb water
easily.
d)
Water travels in long tubes called xylem.
S CIENCE F ACT
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T EACHER ’ S G UIDE 3
6.
e)
Plants use water for photosynthesis and to keep their cells fully stretched.
a)
carbon dioxide
b)
carbon dioxide
c)
oxygen
d)
oxygen
e)
i)
More carbon dioxide is added to the water.
ii)
During the day the water plants are photosynthesizing and adding oxygen to the water which
the plants and water animals are using for respiration. At night the process of photosynthesis
stops while respiration is going on, so carbon dioxide, which is a product of respiration, is
increased.
Workbook 3, chapter 7
1.
a)
oxygen
light energy
taken in from the Sun
given out into the air
water
glucose
absorbed by roots
built up as food
carbon dioxide
taken in from the air
2.
3.
4.
b)
carbon dioxide + water
a)
to soften it
b)
alcohol will catch fire
c)
removes chlorophyll
d)
iodine
e)
blue-black
f)
sunlight
g)
The part that was covered did not receive sunlight therefore it could not photosynthesize and
make starch.
h)
Besides chlorophyll and carbon dioxide, plants also need water for photosynthesis.
a)
So that it receives enough light for photosynthesis to take place.
b)
Bubbles of gas are produced during photosynthesis.
c)
i) oxygen
d)
i)
The rate of the bubbles rising in the tube will slow down.
ii)
Photosynthesis takes place in light.
‡
glucose + oxygen
ii) Test the gas with a glowing splint, it will burst into flame.
Glucose is a type of sugar. It is the ‘food’ made by plants during photosynthesis. A plant can do lots
of things with the glucose it makes.
Some of it will be used straight away to produce energy during respiration.
Some glucose is changed into cellulose to make new cell walls. It gives strong outer coat to plant
cells.
Some glucose will be changed into starch or oil and stored in roots, stems, seeds, and fruits.
Some is joined up with minerals from the soil. Nitrogen, for example, is joined up with glucose to
make protein which is needed for growth.
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a)
Volume of water left in measuring
cylinder in cm3
5.
100
90
80
1
0
2
3
4
5
Time from start in days
6.
7.
b)
It will not give accurate results.
c)
The volume of water in the cylinder reduces.
d)
The concentration of water is more in the cylinder as compared to the plant. Therefore, water is
absorbed by the plant through the roots and carried to the different parts of the plant.
e)
Root hairs increase the surface area for absorption. Their thin walls help to absorb water
quickly.
a)
i)
Its lower leaves are pale green or yellow. Its upper leaves are green.
ii)
Poor root growth.
b)
A plant starved of nitrogen has yellow/green lower leaves, while the upper leaves are pale green
and has a weak stem. A plant starved of magnesium has pale green/yellow lower leaves but the
upper leaves are normal.
c)
By the roots.
d)
Food crops need to have lots of leaves so that they can manufacture lots of starch, that is why
fertilizers containing nitrogen are spread on to fields where food crops are to be grown.
a)
i)
The carbon dioxide level is higher during the night as compared to the day.
ii)
During the day carbon dioxide is being used up for photosynthesis, therefore the level
decreases. Comparatively at night, the plants are respiring leading to an increase in the
carbon dioxide level.
i)
During the day the oxygen levels increase, whereas at night the level decreases.
ii)
At night the plants do not photosynthesize. Instead, they respire along with other animals
thereby taking in oxygen and giving out carbon dioxide. As a result the level of oxygen
decreases at night.
b)
c)
Green plants like algae produce oxygen by photosynthesis and take in carbon dioxide for
photosynthesis. In this way they keep the gases in the atmosphere in balance.
Project
Set up an aquarium in a glass case and observe the activity of the fish and plants in it.
Now answer the following questions:
a) What gas is given out when the fish respire?
b) What gas is taken in when the green plants photosynthesize?
c) What gas is given out when the plants photosynthesize?
d) What gas is taken in when the fish respire?
e) Are the gases dissolved in the water during the day balanced?
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f) What happens at night?
g) Draw a cycle to represent the gaseous exchange between the air, the plants and the fish, during the
day and at night.
Multiple Choice Questions
1.
Which one of the following is not needed in photosynthesis?
A light
2.
B oxygen
A sound energy
3.
5.
6.
7.
B heat energy
B flower
C root
A on a rainy day
B at midday
C in the morning
D working
D seed
D at night
Which pair of facts is wrong?
respiration
photosynthesis
A breaks down food
builds up food
B sets energy free
stores energy
C gives out carbon dioxide
gives out oxygen
D takes place in the dark only
takes place in the light only
Which one of the following is not a function of plant roots?
A take in water
B take in salts
C anchor the plant to the soil
D make food for the plant
Plants need nitrogen to make
B fats
C carbohydrates
D vitamins
The energy for the process of photosynthesis comes from
A glucose
9.
C stored energy
A leaf is tested for starch. When is starch most likely to be present?
A proteins
8.
D carbon dioxide
Which part of a plant takes in carbon dioxide during photosynthesis?
A leaf
4.
C chlorophyll
During photosynthesis light energy is changed into
B the Sun
C air
D soil
Starch reacts with iodine to give a
A blue-green colour
B blue-red colour
C blue-black colour
D blue-yellow colour
10. Carbon dioxide enters the leaf through
A midrib
B stomata
C chlorophyll
D veins
Answers
1.
B
6. D
2. A
3. A
4. B
5. D
7.
8. B
9. C
10. B
A
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C
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hapt
Environmental
chemistry
Unit flow chart
The composition of soil
Looking after the soil
Acid rain
Global warming
What we are doing about it
Aims and learning objectives
•
To show that soils have a variety of characteristics
•
To describe soil and explain how it is produced from rocks
•
To identify the differences between soils
•
To show how the environment is affected by natural processes and human activity
Background information
‘Environment’ is a scientific word for ‘surroundings’. Your environment provides you with such things as
air to breathe, water to drink and a suitable temperature in which to live. These are the physical or the
non-living parts of the environment.
Your life is also affected by other living things. These could be the people in your class, your family, your
pets and even the bacteria in the air.
Living things together with their physical environment form an ecosystem. In an ecosystem many different
processes or cycles take place. These help to keep the environment the same as the years go by. We have
to be careful that we do not upset the balance in our environment.
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Unit introduction
Soil
Ask the students: what is soil? Where did it come from? What is soil used for?
Explain that we see soil about us all the time. It is an essential part of our environment. Without ‘good’
soil farmers cannot grow crops. It is very important to know what soil is and how to look after it.
Discuss the formation of soil and what soil is made up of. Soil is a mixture. It begins life as rock. The
weathering action of wind, water, and ice slowly breaks down the rocks into small particles.
The stages of weathering can be seen in a soil profile. Try digging into the ground with a spade—the
particles should get larger as you get deeper. If you could dig deep enough you would come to solid rock.
Additional activity 1
Take the students out into the school garden and ask them to collect a small sample of soil in a small
box. Show them the different sized particles with the help of a magnifying glass.
Explain that soils are named according to the size of the particles in them. Clay soil is made up of very
small particles, sandy soils contain larger particles.
Rock particles make up the mineral or inorganic ‘framework’ of the soil.
Mixed in with this is humus. This is organic matter made up of the remains of dead animals and
plants. Humus ‘binds’ the rock particles together forming soil crumbs and prevents them from being
blown away too easily by the wind.
Teaching procedure
Investigating a soil sample
Ask the students: what are the constituents of a good
soil? Where do minerals come from? What is humus?
humus
Explain that many of the essential mineral salts needed
by plants come from humus. Humus is the dead remains
of plants and animals in the soil. It is composed of dead
and decaying organic matter, which releases essential
minerals that enrich the soil.
floating particles of clay
Ask the students: where is water found in the soil?
settled particles of clay
Explain that water covers the rock particles in a thin
film. It is from this water film that plant roots take their
water supply. When a soil is saturated with water it is
said to be at field capacity. Clay soils have a high field
capacity. They hold water, and so they are hard to dig
when wet.
silt
sand
gravel
Additional activity 2
Comparing the particle size and field capacity of soils
sand
+
water
loam
+
water
clay
+
water
cotton wool plug
water
water
water
Ask the students: is there air in the soil? How do you know?
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Additional activity 3
Take some garden soil in a beaker and add some water to it.
What do you observe? What are the bubbles that you see?
Explain that the spaces between rock particles in the soil contain air. Any organism living in the soil
requires oxygen and this is provided by the air in the soil. The air spaces are smaller in clay soil.
Ask the students: which is the best type of soil for plants to grow in?
Explain that farmers and gardeners prefer soils that are easy to plough or dig and are fertile. The ideal
soil contains a good balance of clay and sand particles and has a plentiful supply of humus. Such a soil
is called loam.
Looking at organisms in the soil
Additional activity 4
Take some garden soil in a beaker and add water to it. Stir it well and then let it stand on the bench
for a while. What do you observe? What do you find floating on the surface of the water?
Explain that dead organisms and bits of plant material float on the surface of the water.
Ask the students: where do you think animals and plants in the soil go after they die?
Explain that fungi and bacteria are decomposers. They help to break up the dead organisms in the soil.
They produce humus and break it down further to recycle important minerals and improve soil fertility.
Ask the students: have you seen earthworms? Where do they live? Are they useful or harmful for the soil?
Do other animals also live in the soil?
Explain that soil fertility is improved by earthworms. They add humus by pulling leaves down into their
burrows. They also let air into the soil as they tunnel deep into the ground. Worm casts deposited on the
surface of the soil by earthworms ensure the movement of fresh soil to the surface.
Other burrowing animals such as millipedes, a variety of insects, moles, rabbits, and mice all turn the soil
over. They also add to the soil fertility with their droppings and, eventually, their dead bodies. Bacteria and
fungi in the soil also play a vital role in the nitrogen cycle.
Global warming
Ask the students: what is global warming? How is the Earth getting warmer?
Explain that the temperature of the Earth is gradually rising. The reason for this according to scientists is
the increasing amount of carbon dioxide gas in the atmosphere.
Air contains small amounts of carbon dioxide (about 0.03 %). Most of this comes from animal respiration
and of course, carbon dioxide is needed for plant photosynthesis. However, the amount of carbon dioxide
in our atmosphere affects our weather. Short wave radiation from the Sun is absorbed by the Earth. The
warm Earth gives out radiation with longer wavelengths. Although carbon dioxide lets short wave length
radiation pass, it absorbs some of the longer wavelengths. By trapping this energy the carbon dioxide
causes the Earth to heat up. This is sometimes called the greenhouse effect.
Ask the students: do you think the greenhouse effect is useful or harmful for us?
Explain that the greenhouse effect is good for us. Without it the Earth’s average temperature would be
about –45°C instead of the present 12°C. However, in the last 150 years the amount of carbon dioxide in
our atmosphere has risen over 10%. This is mainly because we have been burning fossil fuels such as coal
and oil in our homes and factories. The large increase in carbon dioxide is thought to explain why the
temperature of the northern hemisphere appears to be rising.
Scientists are worried because the rising temperature has caused the polar ice caps to melt at an alarming
rate leading to a rise in the ocean levels causing floods.
If possible show students the movie An Inconvenient Truth. This is a documentary on global warming.
Industry affects our climate in different ways
Ask the students: how does industry affect our climate?
Discuss the various ways of environmental pollution caused by industry.
dust
reflects
solar radiation
temperature
falls
Industry
carbon dioxide
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greenhouse
effect
temperature
rises
Answers
Environmental chemistry: p 72
1.
2.
a)
4.6 billion years old.
b)
It was made from a mass of particles swirling around the Sun.
Characteristics of the Earth:
a)
Surrounded by a thick blanket of gas, the atmosphere.
b)
Mostly covered by water, the oceans.
c)
Rotating non-stop once every 24 hours and continuously orbiting the Sun.
3.
6.5 billion
4.
Humans have exploited natural resources; they are burning fossil fuels and they are causing
environmental pollution.
Soil: p 73
1.
When rocks are weathered by Sun, rain, wind, and frost, tiny grains of rock are broken off. These
grains make up most of the soil on Earth.
2.
a)
Humus is mostly made up of material from dead animals and plants which slowly rot away.
b)
It helps to keep the soil in good condition in different ways, including breaking it down to provide
useful materials which plants use for healthy growth.
3.
Bacteria, fungi, microscopic worms, earthworms, beetles, and moles.
4.
a)
Plants need a constant supply of water, which they get through their roots.
b)
Oxygen is needed by plant roots and by creatures that live in the soil.
a)
mass of freshly dug soil = 155.70g
5.
b)
mass 7 days later
= 132.50g
mass of water in the soil
= 23.20g
volume of freshly dug soil and water
= 1000cc
volume after one hour
= 850cc
volume of air in the soil
= 150cc
Looking after a vital resource: p 74
1.
2.
a)
Clay soils are made up of lots of tiny grains stuck closely together. They have few air spaces and
have water trapped between the grains.
b)
Sandy soils are made up of bigger grains with bigger spaces between them. Sandy soils are light,
easy to dig, and easily drained.
a)
Humus is the dead remains of plants and animals in the soil.
b)
Loam is a mixture of clay, sand, and lots of humus.
3.
Torrential rain and flooding on steep mountain sides can wash the soil off the slopes very easily.
Strong winds can blow away huge amounts of soil.
4.
Planting grass on open land can help prevent soil being washed away by rain or being blown away
by wind.
5.
a)
Fertilizers are chemicals which add mineral salts to the soil.
b)
Plants take up minerals from the soil for their growth, so the soil needs to be replenished by
adding fertilizers.
Acid rain: p 75
1.
From respiration.
2.
The increased burning of fossil fuels all over the world has increased the acidity of rain.
3.
Sulphur dioxide dissolves in rain water producing sulphuric acid which is a strong acid.
4.
sulphur dioxide + water + oxygen ‡ sulphuric acid
5.
a)
Acid rain damages statues and buildings made of limestone or marble.
b)
It corrodes metals and weakens them.
c)
Acid rain makes lake water acidic. This causes aluminium to be released from the soil into the
water. It kills fish and the birds that eat them.
6.
Many modern power stations that burn fossil fuels have scrubbers which remove the harmful gases
from the smoke.
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In many countries, cars, lorries, buses, and trains are fitted with catalytic converters to clean exhaust
gases.
Global warming (1): the cause: p 76
1.
a)
Gases in the atmosphere which keep the heat in are called greenhouse gases.
b)
carbon dioxide and methane
2.
The increasing greenhouse effect is causing the Earth to slowly warm up. This is called global
warming.
3.
Greenhouse gases act like a layer of insulation, keeping heat in. The increased greenhouse effect is
causing the Earth to slowly warm up.
4.
a)
Fewer trees means less photosynthesis, which means less carbon dioxide is taken from the air.
b)
Methane comes from marshy areas, such as where rice is grown.
c)
Methane comes from cattle as they belch and break wind.
Global warming (2): the effects: p 77
1.
More ice in the Arctic and Antarctic will melt. Sea levels will rise as the ice caps melt. Low lying areas
of the world will be flooded.
2.
a)
Some areas will suffer drought; crops will fail, and people will starve.
b)
Mosquitoes and other insects which live in warm places will spread to new areas, possibly carrying
disease.
3.
Locusts are found in hot parts of the world like Africa. However, in the last few years, locusts have
populated southern parts of Europe. Crops there have been decimated.
So what are we doing about it?: p 78–79
1.
Global warming is taking place.
2.
a)
Carbon dioxide levels have been rising since 1860.
b)
The average global temperatures are rising.
3.
Fossil fuels keep a country’s economy going. Factories, transport systems, and power stations all rely
on a steady supply of fuel.
4.
People drive around in big cars, run lots of electrical appliances, and fly around the world on business
and holidays.
5.
We should accept that global warming is a problem; we should try to conserve our natural resources
and we should try to find clean renewable sources of energy.
Test yourself: p 80–81
1.
2.
a)
i)
b)
clay soil
The diagram on the right
sandy soil
ii)
The diagram on the left
smaller particles
bigger particles
less air between particles
more air between particles
holds more water
holds less water
c)
Clay soils can hold more water as their particles are very close to each other therefore they are
called heavy soils.
d)
A mixture of the two types of soil is called loam. It is very good for plants as it holds water as
well as air. It also contains a lot of humus.
a)
i)
They are bigger and heavier particles.
ii)
They are smaller and lighter particles.
iii) Humus contains plant and animal remains which are light in weight.
b)
78
i)
Humus is the dead remains of plants and animals in the soil.
ii)
It is a rich source of minerals in the soil. It also loosens up the particles of a clay soil and
brings together the particles of a sandy soil. It increases the water holding capacity of the
soil.
c)
Loam is a mixture of a sandy and a clay soil, with lots of humus, air, water and mineral
nutrients.
d)
i)
Make terraces to prevent soil erosion due to flooding.
ii)
Grow more trees to prevent soil erosion due to wind.
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a)
carbon dioxide and sulphur dioxide
b)
When they dissolve in rainwater, they produce carbonic acid and sulphuric acid which cause the
rain to become acidic.
c)
i)
They corrode stonework of buildings.
ii)
They kill trees.
iii) They kill the animals living in lakes.
4.
d)
Acid rain can be reduced if we reduce the burning of fossil fuels.
a)
It is used to grow plants in ideal conditions.
b)
A:
Glass lets short wavelength radiation to pass through.
B:
Glass does not let longer wavelengths through.
C: Warm plants and soil emit radiation of longer wavelength.
5.
6.
c)
The Earth is surrounded by air which acts like a layer of insulation, keeping heat in, just as in
a greenhouse carbon dioxide and methane gases are good at keeping heat in. This is why they
are called greenhouse gases. These gases have also been very useful in making the Earth warm
enough for human life to survive.
d)
i)
Burning fossil fuels leads to an increase in the amount of carbon dioxide in the
atmosphere.
ii)
Methane gas comes from marshy areas as well as from cattle as they belch and break wind.
More cattle would mean more methane in the atmosphere.
a)
Trees use carbon dioxide from the air for photosynthesis. If lots of trees are cut, the amount of
carbon dioxide in the air will increase.
b)
Carbon dioxide is a greenhouse gas. It acts as an insulation layer trapping the heat of the Sun
in the atmosphere.
c)
i)
Yes
ii)
The increase in the number of trees will reduce the amount of carbon dioxide in the air, as
they will use carbon dioxide for photosynthesis.
a)
In phase 1
b)
In phase 3
c)
i)
They are used up rapidly.
ii)
Pollution of the environment occurs.
d)
By keeping a check on the use of our energy resources.
e)
We can conserve petrol and gas by cycling instead of driving around in big cars.
Workbook 3, chapter 8
1.
2.
3.
a)
i)
decaying organic matter in the soil
ii)
It helps to keep the soil in good condition in different ways, including breaking it down to
provide useful minerals which plants use for healthy growth.
b)
Plant roots need air to breathe. In a water-logged soil there is no air so plant roots die.
c)
i)
Mass of water lost: 155.7 g – 132.5 g = 23.29 g
ii)
Mass of humus lost: 132.5g – 128.6 g = 3.9 g
a)
rain, wind, and frost
b)
Soils have different colours because they contain different types of minerals in them.
c)
i) Y
a)
i) carbon dioxide
b)
Carbon dioxide dissolved in rain water makes carbonic acid.
ii) X
iii) Z
iv) Z
ii) sulphur dioxide
Sulphur dioxide dissolved in rain water makes sulphuric acid.
c)
Sulphuric acid
d)
i)
When acid rain falls on plants it destroys their leaves and kills them.
ii)
The acid in rain reacts with marble or limestone of buildings and brings about their
corrosion.
e)
We should stop burning fossil fuels and find alternative energy sources.
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4.
5.
6.
7.
a)
Acids in the soil can make the soil more acidic. The ph will be reduced.
b)
1. carrots
2. potatoes
c)
1. yams
2. mushrooms
d)
onions and yams
e)
onions, beans, mushrooms.
a)
A
heat from the sun
B
heat warms the Earth
C
some heat escapes to Space
D
some heat is reflected back
b)
global warming
c)
1 oil
2 natural gas, coal
d)
i) carbon dioxide
ii) from burning fossil fuels
a)
It has increased.
b)
i)
Sea levels will rise causing flooding in the low-lying areas.
ii)
Due to global warming, the polar ice caps will melt causing ocean levels to rise.
c)
1. severe droughts
a)
Unusual, sometimes catastrophic, climatic events such as severe droughts, are forcing the world’s
governments to pay more attention to the dangers of global warming.
2. frequent storms and floods
b)
Fossil fuels keep the economy of a country going. Factories, transport systems, and power stations
all rely on a steady supply of fuel.
c)
i) USA
d)
1. Cut down the use of big cars, aeroplanes, and lots of electrical appliances.
ii) It relies on fossil fuels to keep its economy going.
2. Find clean, renewable sources of energy as quickly as possible.
Project
Make a model of the various causes and effects of pollution and global warming.
•
Explain how dust in our atmosphere reflects some of the Sun’s radiation away from the Earth.
•
Explain how an increase in volcanic activity could cause another ice-age on Earth.
•
Describe one human activity that puts dust into the atmosphere.
•
What are the main causes of dust-domes over industrial cities?
•
How does deforestation put more dust into the air?
•
How does deforestation put more carbon dioxide into the air?
Multiple Choice Questions
1.
The Earth’s atmosphere is about
A 100
2.
B 200
C 300
D 400
Which of the organisms below helps to improve the soil?
A earthworm
3.
km deep.
B scorpion
C lizard
D bee
Soil fertility is commonly increased by
A adding natural or artificial fertilizers to the soil
B continuous cultivation
C allowing cattle to graze on the land
D planting root crops
4.
5.
80
Humus is important because it
A helps prevent erosion
B helps conserve the soil
C adds nitrogen content to the soil
D helps rotation of crops
The capacity of a soil to hold water depends on
A the spaces between the soil particles
B the pH of the soil
C the amount of soil organisms
D the fertility of the soil
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6.
7.
8.
Washing away of soil on slopes by flooding can be prevented by
A building drains or canals
B building terraces
C adding manure
D continuous cultivation
Wind and rain are the main agents that bring about
A soil conservation
B soil erosion
C the breaking up of soil
D the loss of soil minerals
Fossil fuels contain the element
as an impurity, which reacts with the oxygen in the air
to form a gas which causes pollution in the air.
A carbon
9.
B copper
C sodium
D iron
Which two gases are called greenhouse gases?
A hydrogen and oxygen
B oxygen and nitrogen
C carbon dioxide and hydrogen
D carbon dioxide and methane
10. In the last hundred years how many degrees Celsius has the temperature of the Earth’s surface
risen?
A 0.005
B 0.05
C 0.5
D 5.0
Answers
1.
A
6. B
2. A
3. A
4. C
5. A
7.
8. A
9. D
10. C
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C
9
er
hapt
Speeding up
Unit flow chart
What do we mean by speed?
Speed-time graphs
Changing speed and direction
Acceleration
Gravity, falling, and resistance
Aims and learning objectives
•
To understand the concept of speed
•
To show the relationship between forces on an object and its movement
•
To understand the relationship among speed, time, and distance
•
To understand speed-time graphs
•
To explain acceleration and describe how it can be calculated
•
To show the relationship between balanced and unbalanced forces and how these affect the movement
of falling objects
•
To describe how streamlining reduces resistance to speed in air and water
Background information
Whenever we look at the universe we find things that are moving. By studying moving things, scientists
can find laws or patterns which ‘fit’ the movement or motion. This means that they can predict how other
things will move. Forces are thought of as ‘pushes’ or ‘pulls’. The size of a force is measured in units
called ‘newtons’.
Show the students a picture of Sir Isaac Newton and tell them he was an English mathematician and
scientist who, amongst other things, worked to find laws which would explain the movements of planets
and things on Earth. He is remembered now for the ‘laws of motion’ which he set out.
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When an object is pulled by two forces of equal size but in opposite directions, the forces will balance
each other out. Newton realized that a thing will only change its speed or direction of travel when pulled
by a force which is not balanced by other forces.
The best way to understand Newton’s first law is to think of a spaceship moving in outer space so far
from any star or planet that there is no gravity.
The spaceship has no engine to push it but there is no friction or other force to slow it down. It just
travels on and on at the same speed and in the same direction.
The spaceship could be speeded up or slowed down by firing little rockets fixed to it. These would give a
force to change the spaceship’s speed or direction.
Things which are not moving have a speed of 0m/s. These stationary objects obey Newton’s first law too.
Quite simply, as long as there are no balanced forces acting on the object, they will not start to move.
Car designers use these laws to improve the performance of new models. Aerospace engineers use them
to calculate how to put rockets into space and satellites into orbit. Astronomers can find out more about
the universe by observing and measuring how stars move. Athletes can even improve their performances
by studying the science of motion. There is no end to the use which we can make of the laws of motion.
Unit introduction
Speed
Ask the students: what do we mean by speed?
Explain that speed tells us how fast a thing is moving. For example, the speed of a car tells us how fast it
is moving by telling us how far it will move in a set time.
Teaching procedure
Additional activity 1
Look at the car speedometers.
Car 1
Car 2
80 100
60
80 100
60
120
120
40
140
40
140
20
160
20
160
0
km/h
180
0
km/h
180
car speedometers
Car 1 is travelling at a speed of 100 kilometres per hour (km/h). If it stays at this speed it will travel
a distance of 100 km in one hour. Car 2 is travelling more slowly at 80 km/h. At this speed the car
travels just 80 km in one hour.
Distance = speed x time. The speed is useful because we can use it to work out how long a journey
will take.
From the speed and time graph it is easy to work out how far the car will travel.
The table gives some examples of speed, time and the distance travelled.
Speed
Time
Distance travelled
100 km/h
½h
50 km
100 km/h
1h
100 km
80 km/h
½h
40 km
80 km/h
1h
80 km
Time taken =
distance travelled
speed
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Additional activity 2
Fill the blank spaces in the table below.
Distance
Speed
Time taken
200km
100km/h
350km
3½ h
80km/h
200km
½h
80km/h
100km
160 h
Measuring speed
Ask the students: how can we tell how fast a car is moving?
Explain that we have already seen that if we divide the distance travelled by something which is moving,
by the time taken to cover that distance, we get the speed. When measuring speed we can use the
formula: speed = distance/time
Speed-time graphs
Ask the students: how can we represent speed of a moving body in the form of a graph?
Explain that when we make real journeys our speed changes many times. When you get on a train it is not
moving. As it leaves the station it gains speed or accelerates. On a long straight track the train can keep
a constant speed. The driver will need to change the speed as the train approaches bends, level-crossings
and stations. We can show all these variations on a speed time graph. Study the speed-time graph on
page 84 of the student’s book.
One of the things we can work out from a speed-time graph is the distance which the moving object has
travelled.
Draw the speed-time graph for an aircraft at the time of landing on the board.
Speed in m/s
50
10
20
Time in seconds
0
30
Speed -time graph for an aircraft on landing
Explain that the area under the speed-time graph is equal to the distance travelled.
Explain that to calculate the area of any triangle the following formula is used:
Half of its base (b) length multiplied by its height (h): ½ x b x h
For this triangle the area is:
(½ x 30s) x 50m/s = 750m
The runway must be 750m for this aircraft to land safely.
Additional activity 3
The speed-time graph shows the speed of a sprinter in a 100m race.
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Speed in m/s
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
1
2
3
4
5
6
7
8
Time in Seconds
9
10
Speed-time graph for a sprinter
Study the graph carefully and then answer the questions that follow.
a) How long did it take for the sprinter to reach top speed?
b) What was his top speed?
c) What was the sprinter’s speed after one second?
d) What was the sprinter’s speed after two seconds?
e) How far had the sprinter run after four seconds? (Hint: the area under the graph is a triangle)
f) How far had he run after 10 seconds?
Changing speed and direction
Newton’s first law states: ‘Objects will continue to travel in the same direction unless an unbalanced force
acts on them.’
Additional activity 4
Roll a glass marble on a clean glass surface.
Does the marble stop? Does it slow down? Does its speed increase?
When do you think it will stop?
Acceleration
Ask the students: how can we make a moving car move faster?
Explain that by pressing the accelerator we can make it move faster.
Ask the students: how does the car gain speed?
Explain that from a standing start, a racing car can reach a speed of 50m/s in 10 seconds or less. It gains
velocity very rapidly.
Ask the students: what does this mean?
Explain that it means that it gains speed very rapidly. It has a high acceleration.
When an unbalanced force acts on a moving object, in the direction of its travel, the object’s speed
changes. The force may make it speed up but if it is in the opposite direction it will slow the object down.
Acceleration can be shown very clearly on a speed-time graph.
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Car B
Speed in m/s
30
Car A
20
10
0
1
2
3
4
5
6
7
8
9
10 11
12
Time in seconds
The graph has two lines: one for car A and one for car B.
The line for car B is steeper than the line for car A.
A steep slope on a speed-time graph means a large acceleration.
We calculate the acceleration by working out how much the speed changes in one second.
For example, a racing car starts from rest. After 6 seconds it has accelerated to a speed of 30m/s. Its
speed has changed by 30m/s in 6 seconds. In one second its speed would have changed by 30/6 = 5(m/
s)/s
We can say the units as ‘metres per second, per second’. This is because the acceleration tells us how
much the speed has changed (in metres per second) in each second.
acceleration =
change in speed
time taken
Ask the students: what happens when we apply the brakes of a moving car?
Explain that the opposite of acceleration takes place. If a car has a retardation or deceleration of 5 m/s/s
it is losing 5 m/s of speed every second.
Gravitational forces and air resistance
Ask the students: what is gravity? What is the force of gravity?
Explain that gravity is the name given to the force that makes things fall down rather than up. It also
keeps the planets moving in a regular pattern of orbits. Sir Isaac Newton was the first to provide an
explanation for gravitational forces. The main idea that Newton developed was that all objects attract
each other. Objects with a greater mass will attract with a stronger force. These forces act towards the
centre of the object.
Gravitational force
Ask the students: is there an attractive force between you and your chair?
Explain that all the objects around you have tiny attractive forces between them. But these are too small
for you to feel. Because the Earth is so massive, you can feel the force between you and the Earth.
Additional activity 5
Hang something from the end of a spring balance and measure the downward pull from the Earth.
Explain that this pull is called a gravitational force. Weight is another name for the gravitational force
from the Earth.
As weight is a force it is measured in newtons. Most things have several forces acting on them. For
example, everything feels the pull of gravity, and moving things experience friction trying to slow them
down. Sometimes, the forces acting on something all cancel each other out. Then it behaves as if it has
no force on it at all, and obeys Newton’s first law.
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When an acrobat stands on a tight rope, it sags, until the springiness of the rope produces enough
upward force to oppose his weight. As a result the upward force and downward pull on the acrobat’s
body cancel each other out, so the acrobat stays balanced.
Air resistance
Ask the students: have you seen a skydiver fall towards the Earth? Does he fall quickly or gradually? If you
throw a stone up in the air, does it come down quickly or slowly? Why?
Additional activity 6
Throw a stone and a feather from the top of a double storey building.
Ask the students: what happens? Do both things fall down at the same time?
Explain that air resistance slows down some things more than others. It does not slow down a falling
stone very much, but it slows a feather a lot. Without air resistance, all things falling near the Earth would
have the same acceleration of 10m/s/s. This is the acceleration of free fall, g.
So, without air resistance, anything dropped would speed up like this:
0s
no speed
After 1s
10m/s
After 2s
20m/s
After 3s
30m/s
And so on.
Ask the students: why does air resistance slow things down?
Explain that when cars, bicycles, and other things try to move in a particular direction, there is a force
against them called air resistance. This is because air is made up of gases. The molecules in these gases
bump into moving objects causing a force against the motion. At low speeds this is only a small force. At
higher speeds it becomes much larger.
Ask the students: can we reduce air resistance in some way?
Explain that air resistance can be reduced by using shapes which let air ‘slip’ past more easily. This is called
streamlining. Now that we understand friction and air resistance we can see how Newton’s first law applies.
Explain that to accelerate, the force from the engine must be bigger than the forces of friction and air
resistance put together.
At a steady speed, the forward force will just balance the forces of friction and air resistance.
To stop a car the driver takes his foot off the accelerator pedal. This reduces the force from the engine.
He also puts on the brakes. This makes the friction much larger.
Ask the students: how does a heavy object such as an aircraft lift up and move in the air?
Explain that the weight of an aircraft moving through the air at high speed is balanced by the upward
force exerted by air on the wings of the aircraft. The resistance of the air is balanced by the thrust from
the engine. The forces all cancel, so the aircraft keeps moving at a steady speed in a straight line.
Terminal velocity
Ask the students: how does a sky diver land gently to the ground?
Explain that as a skydiver falls, the air resistance increases as her speed rises. Eventually, air resistance is
enough to balance her weight. If she weighs 500 newtons, then the air resistance rises to 500 newtons.
She stops accelerating and falls with maximum speed called her terminal velocity.
If air resistance balances the skydiver’s weight, why doesn’t she stay still? Explain that there wouldn’t be
any air resistance unless she was moving.
Ask the students: surely her weight is greater than air resistance if she is travelling downwards?
Explain that if it were, she would gain speed, instead of keeping a steady speed.
Additional activity 7
A skydiver weighing 600N falls through the air at a steady speed of 50m/s.
a) Draw the diver, showing the forces acting on him.
b) What name is given to his steady speed?
c) What is the air resistance on him in newtons?
d) What is his mass?
e) Why does he lose speed if he opens his parachute?
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Answers
Speeding up: p 82
1.
The planets of the solar system orbit the Sun at a constant speed.
2.
a)
They evaporate.
b)
They freeze.
3.
To catch its prey; to run away from its enemies.
4.
Plants move towards sunlight.
5.
Scientists need to control the machines that they make.
What do we mean by speed?: p 83
1.
2.
3.
4.
a)
1.66m/s
b)
1.43m/s
c)
1.66m/s
d)
1.73m/s
a)
1000km
b)
100km
a)
2 hours
b)
3.5 hours
a)
1200m
b)
0.25s
Speed-time graphs: p 84
1.
a)
i) accelerating
b)
30m/s
c)
25s
d)
10s
e)
30m/s
f)
30m/s
ii) moving at constant speed
iii) slowing down and coming to a stop
Changing speed and direction: p 85
1.
When the forces acting on a body cancel each other out and the body does not move, we say that the
forces are balanced.
2.
When the forces acting on a body are not equal, we say that the forces are unbalanced. The body
moves in the direction of the greater force.
3.
Newton’s first law of motion states that:
If something has no force acting on it, it will stay still if it is still, or if it is moving at a steady speed,
it will stay moving at a steady speed in a straight line.
4.
The spacecraft does not need an engine to push it because there is no friction to slow it down; it just
travels on at the same speed in the same direction.
Acceleration: p 86
1.
It means that the speed of the car is increasing by 4 metres every second.
2.
a)
12m/s
b)
4s
c)
0m/s2
d)
0 to 6m/s
e)
3m/s2
f)
7s
g)
(12 + 10 + 5 + 0) / 4 = 6.75 m/s2
Gravity, falling and air resistance: p 87
88
1.
The weight of the object makes it accelerate to the ground.
2.
a)
The frictional force produced by air molecules is called air resistance.
b)
The steady speed at which a body falls is called its terminal velocity.
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3.
Skydivers spread out their bodies so that their weight is balanced by air resistance.
4.
Gravity makes all falling objects accelerate towards the centre of the Earth, but air resistance is a force
opposing this motion. Air resistance depends upon the size and shape of an object and its speed.
In order to practice parachuting, larger parachutes help beginners to land gently at a steady low
speed.
5.
A small parachute will cause less air resistance and the parachutist will fall at greater terminal velocity
than that of a large parachute.
Test yourself: p 88–89
1.
a) 6km/h
2.
a)
b) 9km/h
c) 45 minutes
Speed in m/s
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
9
10
Time in seconds
The distance travelled by the driver can be found by calculating the area under the speed-time
graph.
a)
i)
unbalanced
ii)
The forces are unbalanced because the forward force is greater than the backward force.
i)
The car would move.
ii)
Since the forward force is greater than the backward force, the car will move forward.
b)
c)
4.
i) forwards
ii) 1500 N – 1000 N = 500 N
a)
Change of speed = 20m/s
24
Speed in m/s
3.
b)
20
16
12
8
4
0
1
2
3
4
5
6
Time in seconds
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5.
6.
b)
acceleration = 20/5 = 4m/s2
c)
i) 24m/s
d)
Since we have calculated the acceleration of the car, we can easily and accurately calculate its
speed after 50 seconds, instead of predicting it.
a)
i) 25m/s
b)
100/3 = 33.33m/s2
c)
1s
d)
450m (area under the graph)
ii) 32m/s
iii) 40m/s
ii) 50m/s
iii) 100m/s
speed = acceleration x time taken
= 3m/s2 x 27s = 81m/s
7.
a)
terminal velocity
b)
air resistance
weight
c)
The weight of the parachutist accelerates him towards the ground. Comparatively, the opposite
force reduces the speed of the falling body until both forces are balanced. When this condition
is reached, the parachutist falls at a steady speed.
d)
The parachutist’s weight is balanced at a low speed by the parachute’s air resistance.
Workbook 3, chapter 9
1.
a)
i) 8m/s
ii) 8m/s
iii) 8.33m/s
b)
In 1 hour the snail travels 50cm.
In 2 hours it travels 50 x 2 = 100cm = 1m
2.
3.
4.
90
c)
i) 2 hours ii) 15 minutes.
a)
It is accelerating.
b) It is moving at a constant speed.
c)
It is slowing down.
d) It has stopped.
a) 10s
b) 30m/s
c) 10s
e)
i) 150m
ii) 450m
iii) 525m
a)
air resistance and road friction
b)
i) in diagram 2
c)
It will increase.
d)
i) diagram 1
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d) 15m/s
ii) The bicycle travels at a steady speed.
ii) The forward force is greater than the air resistance.
T EACHER ’ S G UIDE 3
5.
6.
7.
a)
Girl 2
b)
Girl 1
c)
5s
d)
7m/s
e)
This means that her speed is changing at the rate of 2m/s in every second.
a)
gravity
c)
Air resistance becomes greater than the force of gravity.
d)
The air resistance slows down the sky diver as she reaches the ground. The slow speed helps her
land on her feet rather than crash into the ground.
b) air resistance
If a block of iron is hung from a piece of string, the downward force (weight) is balanced by an
upward force in the string (tension). The iron block stays at rest. If the string is cut, the weight
makes the block accelerate downwards. On Earth, gravity makes falling objects accelerate at about
10m/s2. This means that after 1 second the block will be falling at 10m/s, after 2 seconds it is falling
at 20m/s2, after 30 seconds it is falling at 30m/s and so on. This is only true if objects are falling
in a vacuum.
Project
Try to find out about Sir Isaac Newton:
a) When was he born? When did he die?
b) Which university did he study at?
c) What was the name of the book which contained his laws of motion? When was it published?
d) What other scientific work did he do?
e) What did he have to do with:
i) the Houses of Parliament ii) the Royal mint?
Multiple Choice Questions
1.
A truck takes 20s to travel a distance of 80 m. What is its speed?
A 1m/s
2.
A 5m
3.
4.
5.
C 3m/s
D 4m/s
B 30m
C 90m
D 180m
Acceleration can be calculated using the formula
A average speed x time
B change in velocity/time
C distance/time
D force x mass
A ball falls freely with no air resistance toward the surface of the Earth. Which quantity remains
constant?
A acceleration
B distance travelled in 1s
C speed
D velocity
A cyclist riding at a speed of 5 m/s braked with uniform deceleration and stopped in 3m. How long
did she take to stop?
A 0.6s
6.
B 2m/s
A car starts from rest and is uniformly accelerated to a speed of 30m/s in 6s. What is the distance
travelled by the car?
B 1.2s
C 1.33s
D 3.0s
Why does an object falling in the Earth’s gravitational field reach a steady velocity?
A air resistance increases with an increase of velocity
B the Earth’s gravitational field decreases as the object falls
C the mass of the object remains constant
D the weight of the object increases as it falls
7.
A spacecraft moving in outer space is far away from the effects of:
A speed
B gravity
C acceleration
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8.
Newton’s first law states that if something has no
A force
9.
B gravity
C friction
A initial
B final
C terminal
B time
C gravity
Answers
D
6. A
2. C
3. B
4. A
5. B
7.
8. A
9. C
10. B
B
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D zero
it is easy to work out the distance travelled.
A weight
92
D acceleration
When air resistance balances the weight of a falling sky diver, the person falls at a
velocity.
10. From the speed and
1.
acting on it, it will stay still.
FILE
T EACHER ’ S G UIDE 3
D friction
C
10
er
hapt
Where does our
food come from?
Unit flow chart
Fertilizers
Too much fertilizer
Competition
Knocking out the competition
DDT
Creating perfect conditions for plant
growth
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Aims and learning objectives
•
To show that humans are part of a complex food web
•
To show the factors affecting plant growth
•
To identify a range of minerals that plants need for healthy growth
•
To describe how the overuse of fertilizers can affect the environment
•
To describe competition between plant crops and weeds
•
To describe how treating fields with pesticides can affect food webs
•
To suggest an alternative to the use of pesticides
•
To describe the advantages of growing crops in greenhouses
Background information
Carbon, oxygen, nitrogen, and water circulate in the environment. Even though they continuously change
from one form to another, these materials stay in roughly the same proportions within ecosystems.
Energy, however, does not cycle. Instead it flows through ecosystems in a straight line.
Producers convert the light energy from the Sun into chemical energy in sugar molecules. Some of this
energy is used by plants in respiration, while the rest is stored as starch or used to build other chemicals
like proteins and fat. When consumers feed on plants they release this stored energy by digestion and
respiration. They can use it for activities such as movement. Some energy, however will be ‘locked up’ in
the animal’s body in fat and protein. This whole process is repeated at each link in a food chain. In the
end all the energy is ‘lost’ usually as heat, to the environment. The trapping of energy from the Sun by
producers maintains a continuous flow of energy through ecosystems.
Unit introduction
The more people there are in the world, the more food is required to feed them. As the world population
increases so too does the demand for efficient farming methods. Farmers must get the highest yields that
they can.
Teaching procedure
Ask the students: what farming methods do farmers employ to increase the yield of crops?
Explain that in order to produce more food crops, farmers add fertilizers to the soil.
Ask the students: why is the excessive use of fertilizers harmful?
Explain that unfortunately, fertilizers do not just help the crops to grow. Other plants grow better as well.
These other plants compete with the food crop for light, water, and minerals.
Ask the students: what do farmers do to get rid of weeds?
Explain that to improve the chances of success for the food crops, chemicals are used to kill the unwanted
plants (weeds). These chemicals are called selective weed-killers or herbicides because they kill the weeds
without harming the crops.
Ask the students: what are fungicides? Why are they harmful?
Explain that fungicides are used to kill any fungal competitors that may also affect the successful growth
of food crops. A fungus called wheat rust feeds on living wheat plants as they grow. This reduces the
amount of wheat produced.
Ask the students: which animals spoil food crops?
Explain that there are animal competitors, too. Small mammals such as mice eat the crop before and after
it is harvested. Insects present a much greater problem. In some parts of the world one-third of all food
crops are eaten by insect pests. Chemicals have also been developed that kill insects. These chemicals are
called insecticides.
Messing about with food chains
Ask the students: how does man interfere in natural food chains?
Explain that the development of new high-yield cereals has helped to meet the increasing demand for
food. However, these new cereals need much more fertilizer than the older varieties. This has caused
another serious problem for food chains.
Modern artificial fertilizers are soluble. Therefore much of the fertilizer used on the land gets washed
away into nearby streams, rivers, and lakes, where they break food chains and cause fish and other
aquatic animals to die.
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It is possible to see the effect fertilizers have on water ecosystems by studying the kinds of animals
living there.
Additional activity 1
Study the table carefully and then answer the questions below:
Amount of pollution
Animals present
Volume of oxygen (cm3/litre of water)
clean water
mayfly nymph, stonefly
nymph, salmon, trout,
6.5 to 9
little pollution
caddis fly larva,
shrimp, trout rarely
6 to 6.5
some pollution
water louse, blood
worm, leech, poor
fishing
3.5 to 4
heavy pollution
sludge worm, cat-tailed
maggot, no fish
2.5 to 3.5
Questions
1. List three fish which you would expect to find in a river with a high level of oxygen.
2. Roughly how much oxygen would you expect to find in a river that had no fish at all?
3. Suggest how the pollution of waterways by fertilizers could be reduced?
Competition
Ask the students: what is competition? Is there competition between plants; between animals?
Discuss that in any ecosystem there are always more organisms produced than can ever survive.
Competition takes place between organisms of the same species and between organisms of different
species.
Ask the students: which organisms do you think will survive?
Explain that only those best adapted to their environment will survive.
Ask the students: what do plants compete for?
Explain that plants make energy available to other organisms by ‘trapping’ it from sunlight. Plants
must therefore try to get as much light as they can in order to make as much food as possible. This
competition for light can be seen in a wood. The faster growing trees win the race.
Ask the students: what other things are necessary for the healthy growth of plants? Why?
Explain that water and mineral salts are essential for plant survival. Food cannot be made without them.
Plants with root systems that spread deeper and wider in the soil will be more likely to survive at the
expense of those with smaller roots.
Ask the students: why do plants produce flowers?
Explain that bright sweet-smelling flowers attract insects. The more insects that visit a flower, the more
chance the plant has of pollinating other flowers and therefore reproducing itself.
Ways of knocking out the competition
Ask the students: how can a farmer knock out competition?
Explain that greenfly feed on roses. A rose grower needs to protect his or her plants against a greenfly
attack. Insecticide sprays are often the only answer. They kill the insects and the plants grow to produce
flowers that the grower can sell.
Ask the students: are insecticides useful or harmful for plants?
Explain that insecticides are harmful for plants and the environment, especially when used incorrectly.
Ask the students: so what can a rose grower do?
Explain that the answer lies with the ladybird. If ladybirds are released on to rose plants, they eat all
the greenfly and the roses are saved. Ladybirds are used to control the number of greenfly. This is an
example of biological control. Discuss some other examples of biological control.
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Whitefly damage food crops such as tomatoes. They are a particular menace in greenhouses where
conditions are ideal for their rapid growth—warm, moist, and with plenty of food. The parasite wasp is an
insect which lays its eggs inside the larvae of the whitefly. When the eggs hatch they slowly feed on the
larvae, eventually killing them. No whitefly larvae means no adult whitefly.
Ask the students: in what way are insecticides harmful for us?
Explain that people are becoming more concerned about the use of insecticides on food, especially those
which are eaten raw, like tomatoes.
Ask the students: how can we control the use of insecticides?
Explain that biological control agents such as the parasitic wasp can provide an acceptable alternative to
insecticide spraying. To be really effective, the predator used for biological control must be able to find
its prey easily. Also, it should only feed on one kind of prey.
Scientists have to carry out many tests in the laboratory before releasing any biological control in the
environment.
Additional activity 2
Give two important characteristics that make a predator a suitable agent for biological control.
What do you suppose happens to the ladybirds when they have removed all the greenfly from the rose
grower’s crop?
What might happen if ladybirds also fed on roses, or whitefly parasites took a liking to tomatoes?
Why must scientists carry out many tests on new biological control agents before releasing them into
the environment?
Answers
Fertilizers: p 91
1.
Farmers add mineral elements to their soils in the form of fertilizers.
2.
Natural fertilizers are made from plant and animal wastes such as sewage sludge, animal manure, or
compost. Artificial fertilizers are chemical substances which contain the elements essential for plant
growth.
3.
sewage sludge, animal manure, compost
4.
NPK fertilizers contain three main nutrients: nitrogen (N), phosphorus (P), and potassium (K).
5.
a)
Nitrogen is essential for making new plant tissue.
b)
Potassium is essential for flower and fruit growth.
c)
Phosphorus is essential for proper root growth.
d)
Magnesium is essential for chlorophyll formation.
a)
It has yellow leaves and weak stems.
b)
It has poor flower and fruit growth.
c)
It has poor root growth.
d)
Leaves turn yellow from bottom upwards.
6.
Too much fertilizer: p 92
1.
They need much more fertilizer than the older varieties.
2.
Modern artificial fertilizers are soluble. Therefore, much of the fertilizers used on the land are washed
into nearby streams, rivers, and lakes.
3.
The large amounts of nitrogen, phosphorus and potassium in the water encourage the growth of algae,
which forms a thick green blanket over the surface of the water. Light cannot pass through to the
water plants below so they die. Bacteria decompose the dead plants using up oxygen in the water. Less
oxygen causes fish and other aquatic animals to die. With fewer animals to eat the algae, it grows even
faster. When the algae eventually dies, bacteria decompose the remains using up all of the oxygen.
4.
a)
The process by which the water ecosystem in a pond or river dies, due to the addition of artificial
fertilizers to fields, is called eutrophication.
b)
All the life in a pond or river eventually dies. This means that the water ecosystem dies.
5.
96
Sewage contains an excellent source of food for bacteria as well as phosphates from household
detergents. If sewage is not treated before removing the phosphates and detergent, chemicals from it
will provide an excellent breeding ground for bacteria which will multiply rapidly causing eutrophication
very quickly.
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Competition: p 93
1.
Plants compete for space, sunlight, water, and mineral salts.
2.
a)
Fast growth helps them to reach sunlight faster than other plants.
b)
A deep and wide root system helps plants to absorb more water as compared to plants with
smaller roots.
c)
Brightly coloured flowers help the plant to make seeds by insect pollination.
a)
Unwanted plants among cereal crops growing in a field are called weeds.
b)
Weeds compete with the crop plants by taking valuable nutrients from the soil and restricting the
growth of the crop.
3.
4.
Plants cannot hide from predators or shelter from bad weather.
Knocking out the competition: p 94
1.
a)
i)
Herbicides are chemicals which are selective weed-killers. They are used to kill weeds without
harming the crop.
ii)
Fungicides are used to kill any fungal competitors that might affect food crops.
iii) Chemicals called insecticides have been developed to kill insects.
b)
They are called pesticides because they kill pests.
2.
Farmers must produce the highest crop yields they can.
3.
Problems of using pesticides:
4.
•
Some pests are resistant to them.
•
They have to be used over and over again as their effect does not last long.
•
Useful insects such as ladybirds and bees are killed along with the pests.
•
People are becoming concerned about pesticides in their food.
•
Pesticides can cause pollution and seriously affect food chains.
a)
The use of pesticides can be reduced by encouraging the natural predators of insect pests.
b)
Biological control has advantages over pesticides:
•
The pest does not become resistant to the predator.
•
The predator usually feeds only on one kind of prey.
•
There is no need to replace the predators—they breed themselves.
DDT—a bad insecticide: p 95–96
1.
6g
2.
barn owls
3.
Birds living over water have higher levels of DDT in their bodies because it is not biodegradable. It is
absorbed in the bodies of the fish, which have absorbed DDT from the bodies of insects and smaller
animals in the food chains.
4.
Levels of DDT sprayed on the crops build up in the soil, from where it finds its way into streams and
rivers and the oceans. As it is passed from consumer to consumer, it is stored in the fat layers of
their bodies. Wood pigeons and moorhens do not absorb much DDT as they eat small insects which
absorb small quantities of DDT sprayed on crop plants.
Creating perfect conditions for plant growth: p 97
1.
Plants need light, water, carbon dioxide, minerals, and suitable temperature for healthy growth.
2.
A greenhouse is a building, usually made of glass, used to grow crops under best conditions.
3.
A green house protects plants from wind, rain, and pests such as insects and birds.
4.
They prevent cross-pollination with plants growing in the wild, which is an advantage when growing
genetically modified crops.
5.
Plants use red and blue parts of the spectrum for photosynthesis.
6.
It prevents the cross-pollination of the genetically modified crops, so the new variety that is being
produced should have the characteristics which the farmer wants in his crops.
Test yourself: p 98
1.
a)
In the producer.
b)
Energy loss decreases down the food chain.
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2.
c)
Plants have the maximum amount of energy. Energy is lost at each link in a food chain.
d)
The number of herbivores which human beings eat would increase and the plants on which the
herbivores feed would be greatly reduced.
a)
i) The soil.
b)
Leaves turn yellow from bottom upwards.
c)
Artificial fertilizers containing nitrates and phosphates are important for plant growth and for
fruit and seed development.
d)
They are an excellent source of food for them.
ii) Plants absorb them by their roots.
3.
algae ‡ shrimps ‡ fish ‡ sea otters
4.
a)
Plant A
b)
It can avoid competition for light.
c)
It can reach water more easily.
d)
i)
Plant A
ii)
It grows quickly and has a spreading root system which helps it to overcome competition
with other plants.
5.
6.
a)
approximately 200
b)
More than 5000
c
The biological control organisms reproduced and multiplied, feeding on the pests.
d)
i)
About 12 months
ii)
The pests are also reproducing and multiplying.
a)
As the intensity of light increases the rate of photosynthesis also increases.
b)
Light provides the energy that is needed for photosynthesis to take place.
c)
The rate of photosynthesis would be increased.
d)
Without leaves, it is easier for pollination and fertilization to take place.
Workbook 3, chapter 10
1.
The transfer of energy along the food chain is very inefficient. There is about 98% energy loss
between the Sun and producers, and about 90% energy loss between producers and consumers. There
is another 90% loss of remaining energy when a secondary consumer eats a primary consumer. This
energy loss could be reduced if people were to eat food from nearer the beginning of the food chain.
Eating plants instead of the animals that feed on them makes better use of the available energy.
2.
a)
Height of seedlings in mm
30
with fertilizer
25
20
15
without fertilizer
10
5
1
0
2
3
4
5
Time in days
98
b)
14mm
c)
More than 3 days.
d)
Fertilizers are chemicals that are necessary for the growth of plants.
e)
Seedlings which were given fertilizer grew at a much faster rate.
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3.
4.
5.
6.
7.
a)
It is washed away from fields with the rain water.
b)
Algae feed on the fertilizer and grow rapidly.
c)
Light cannot pass through the water to the plants below, so they die.
d)
Bacteria decompose the dead plants using up the oxygen in the water. Less oxygen causes fish
and other aquatic animals to die.
e)
eutrophication
a)
They are orange in colour.
b)
The predatory mites feed on the spider mites. This way they will help protect the tomato plants
from being eaten by the spider mites.
c)
This method is useful because the pest does not become resistant to the predator; the predator
usually feeds on only one kind of prey; there is no need to replace the predator—they breed
themselves.
d)
In open fields there are other predators of orange predatory mites.
e)
biological control
a)
It kills insects.
b)
A material which can be broken down by bacteria and fungi is called biodegradable.
c)
It accumulates in the organisms in a food chain.
d)
As DDT passes along the food chain it accumulates in the fat layers of the animal’s body. As time
passes, the concentration of DDT increases in the grebe’s body.
e)
As the concentration of DDT reaches its peak, ultimately the grebe will die.
a)
i) A
b)
It can absorb more water and mineral salts.
c)
i)
for reproducing their species
ii)
It can produce flowers and seeds faster than the other species.
ii) It can reach light faster.
a)
A greenhouse is a house made of glass which can provide plants with all the necessary conditions
for them to grow and reproduce.
b)
i)
The supply of carbon dioxide is controlled and it is free from impurities.
ii)
Maintains a constant temperature.
iii) Provides light even on cloudy days.
c)
i)
The amount of minerals.
ii)
Plants in a greenhouse are grown in water cultures to provide them with the correct amount
of minerals for their healthy growth.
Project
Controlling the environment
Discuss the perfect conditions for plant growth.
How can plants in a greenhouse be protected from very high temperatures, very low temperatures?
There are several different kinds of automatic watering systems for greenhouses. Find out how one of
these works, then try to design your own system.
Multiple Choice Questions
1.
Which element is needed by plants to make new plant tissue?
A nitrogen
2.
A sewage
3.
C phosphorus
D magnesium
C NPK
D compost
causes poor flower and fruit growth in plants.
B potassium
C phosphorous
D magnesium
The process which causes all life in a pond or river to die is called:
A flocculation
5.
B sludge
The deficiency of
A nitrogen
4.
B potassium
Which one of the following is not a natural fertilizer?
B eutrophication
C respiration
D transformation
Plants growing in a field of cereal crop are called:
A seeds
B feeds
C weeds
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6.
Herbicides are chemicals which are used to kill
A insects
7.
B weeds
C birds
D animals
What is the greatest disadvantage of using DDT as an insecticide?
A it is used to kill off many of the insects which attack food crops
B it kills lice
C it is not biodegradable
D it kills mosquitoes
8.
One of the problems with the use of pesticides is that:
A they are non biodegradable
B they are selective weed killers
C they kill fungal competitors that might affect food crops
D they kill insects
9.
Why do moorhens and wood pigeons have low level of DDT in their muscles?
A they are carnivores
B they are herbivores
C they are omnivores
D they eat fish
10. Which colours of the spectrum do plants use for photosynthesis?
A violet and indigo
B blue and green
C yellow and red
D red and blue
Answers
1.
A
6. B
100
2. C
3. B
4. B
5. C
7.
8. A
9. B
10. D
C
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Using chemistry
Unit flow chart
Burning fuels
Chemical reactions as energy
sources
New materials through chemistry
Conservation of mass
Aims and learning objectives
• To extend the knowledge about how chemical reactions can be used as energy sources
• To identify a range of fuels as substances that release energy as they burn
• To explain the difference between complete and incomplete combustion
• To show how chemical reactions are used to make new materials
• To recognize that mass is conserved in chemical reactions
• To explain the apparent loss in mass in chemical reactions involving the production of gases
Background information
Wood, charcoal, and coal are all fuels which contain carbon. Carbon is a chemical element found in
all living things. It is also found in minerals like coal. There are several different forms of carbon. The
graphite used inside a pencil is a form of carbon and so is diamond.
Unit introduction
Combustion
Ask the students: what is combustion?
If you hold a piece of paper next to a lighted match, the paper catches fire and burns. You see a flame, some
smoke and then nothing but ashes. The paper has disappeared. Whenever you make a fire, you bring about
a chemical change called burning or combustion. When a material burns, it combines with oxygen and gives
off heat and light. In burning or combustion, the material that burns disappears. One or more materials with
different properties take its place.
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Teaching procedure
Additional activity 1
Heat some powdered coal in a test tube.
Ask the students: what happens?
Explain that when powdered carbon is heated it glows red hot as it reacts with oxygen in the air. When
burning carbon is put into pure oxygen, it flares up with sparks and a bright flame. The bright flame
and hot sparks show us that the burning carbon is giving out heat. After the flame goes out, the gas
produced by burning carbon can be tested.
Now pour some calcium hydroxide solution (lime water) into the gas jar.
Ask the students: what happens to the lime water? What does this tell us?
Explain that the clear liquid turns a milky white colour. This test tells us that the gas produced is carbon
dioxide.
Write the equation for combustion of carbon on the board.
carbon + oxygen ‡ carbon dioxide + heat
It is this reaction which makes charcoal and coal good fuels.
Ask the students: what is an exothermic reaction?
Explain that exothermic means that heat is given out. The gas in the gas jar can be tested by putting
some wet, blue litmus paper in the top of the jar. It turns a purple-red colour showing that carbon dioxide
dissolves in water to give a weak acid.
Carbon dioxide + water ‡ carbonic acid
Incomplete combustion
Ask the students: which gas is produced by burning coal?
Explain that usually when carbon burns, carbon dioxide is formed. If, for some reason, there is not
enough oxygen available, another gas is produced. This is carbon monoxide.
Write the equation on the board and explain that it shows how carbon burns in a limited supply of
oxygen. Notice how two carbon atoms react with just one oxygen molecule:
2 carbon atoms + 1 oxygen atom ‡ 2 carbon monoxide atoms
In a confined space carbon monoxide can be very dangerous, because it is a highly poisonous gas. Can
you think of a way in which people in our country die of carbon monoxide poisoning?
Chemical reactions
Ask the students: what is a chemical reaction? Discuss some familiar chemical reactions.
Explain that some chemical reactions are very fast. They only take fractions of a second to happen.
Explosions are very fast reactions. Other chemical reactions such as the ripening of fruit, can take days
or even months. The rate at which chemical reactions take place can be measured very accurately. In
industry it is important to be able to develop a substance in the most economical time possible.
Ask the students: can the rate of chemical reactions be controlled?
Explain that there are many ways in which the rate of a reaction can be controlled.
Discuss why in many industrial processes it is important to produce a chemical as cheaply and as quickly
as possible.
Ask the students: what factors do you think are important for the efficient production of a chemical?
Explain that the concentration of chemicals, temperature of reaction, pressure, and the use of catalysts
are the factors which are important in the efficient production of a chemical.
Exothermic reactions
Ask the students: what is an exothermic reaction?
Additional activity 2
Take some powdered iron and add copper(II)oxide to it. On heating, the reaction starts. The mixture
glows, even after the Bunsen burner is removed. This reaction is an exothermic reaction. It means that
heat is given out during this reaction.
Electrical energy from a chemical reaction
Ask the students: how is electricity generated by a car battery?
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Explain that a battery cell consists of two different metals and an electrolyte. In the cell, chemical energy
produces electricity. The more reactive metal becomes the negative pole. Electrons flow from the negative
pole.
Additional activity 3
Two copper strips are connected to a light bulb and placed in a solution of sodium chloride. The
solution is an electrolyte—it can conduct electricity. What happens?
Replace one copper strip by a magnesium strip. What happens?
Replace the bulb by a voltmeter. What do you observe?
How is electricity produced in the second experiment?
Where do the electrons come from?
Explain that magnesium can give up more readily than copper. So magnesium atoms give up electrons
and go into solution as ions. The electrons flow along the wire to the copper strip. This arrangement is
called a Voltaic cell. The magnesium strip is the negative pole of the cell. The copper strip is the positive
pole.
The further apart the metals are in the reactivity series, the higher the voltage of the cell.
New materials through chemistry
Take a look around you at clothes, furniture, and equipment. Spend a few moments thinking what some
of the things are made from, and how they are made.
Explain that before 1856 all the substances used in making things were natural. They came directly from
plants, animals or the Earth.
Then a young chemistry student called William Perkin made a breakthrough which was to be the start of a
huge industry.
While he was investigating coal tar, he produced a new substance which could be used to dye cloth
purple. He called it mauveine, and became rich very quickly by supplying it to the textile industry.
Mauveine was the first of many synthetic substances to be created. Synthetic means something that is
made rather than occurring naturally. Today synthetic materials, such as plastics, are used for many
purposes, and their production is a huge international industry.
Packaging
Ask the students: why are soft drinks expensive to buy?
Explain that young people buy billions of soft drinks each year. Drinks would be much cheaper if you
could buy only the drink. But of course you need the container too. Aluminium cans, tin cans, glass and
plastic bottles, and paper cartons are all popular methods of packaging.
Glass bottles
Ask the students: what is glass made of?
Explain that glass is a compound called sodium silicate. To make glass, silicon oxide (from sand) and
sodium carbonate are heated in a furnace to 1500°C. Scrap glass that is being recycled is added to the
mixture. The silicon oxide and sodium carbonate react to form sodium silicate.
silicon oxide + sodium carbonate ‡ sodium silicate
The red hot molten glass oozes through pipes in the bottom of the furnace tank. It is chopped into short
lengths and dropped into the moulding machine below the furnace. Compressed air is then blown into the
moulds to blow the glass into the shape of the moulds.
Plastic bottles
Ask the students: what are plastic bottles made of?
Explain that plastic materials all use oil as their raw material. Ethene, whose molecules consist of 2 carbon
and 4 hydrogen atoms, can be obtained from oil. Under high pressure and temperature, ethene molecules
join up to make a chain. The new molecule is called polyethene (‘poly’ means many). This consists of long
chains of carbon and hydrogen atoms. The long chain molecules are typical of plastics, and are called
polymers.
The latest plastic bottles used for containing fizzy drinks are made from Polyethylene Terephthalate (PET
for short).
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Conservation of mass
Write any of the following simple chemical equations on the board.
2H2 + O2 ‡ 2H2O
Mg + O2 ‡ 2MgO
C + O2 ‡ CO2
H2 + Cl2 ‡ 2HCl
Zn + H2SO4 ‡ ZnSO4 + H2
Ask the students: does mass of substances change during a chemical reaction?
What does the equation tell you?
Look at the following chemical reaction:
When carbon burns in oxygen, the equation for the reaction is:
C + O2 ‡ CO2
1 carbon atom reacts with 1 molecule of oxygen to give 1 molecule of carbon dioxide
Does the mass change during the reaction?
Now look what happens to the total mass, during the reaction.
Mass of carbon = 12 atomic mass units (amu) or 12g
Mass of oxygen = 16 amu, mass of 2 oxygen molecules = 32 amu or 32g
Mass of carbon and oxygen at the start of the reaction =12 + 32 = 44g
Mass of the carbon dioxide produced at the end = 12 + 32 = 44g
The total mass has not changed during the reaction because the atoms taking part have not changed
either.
The law of conservation of matter states that:
During a chemical reaction, atoms do not disappear and new atoms do not form. The atoms just get
rearranged.
Additional activity 4
The reaction between magnesium and oxygen is:
2 magnesium + O2 ‡ 2 MgO
Write a word equation for the reaction.
How many atoms of magnesium react with oxygen?
How many atoms of oxygen react with magnesium?
Calculate how many grams of oxygen react with:
i)
48g of magnesium?
ii)
12g of magnesium?
(the relative atomic mass of magnesium is 24, and that of oxygen is 16)
Answers
Using chemistry: p 100
1.
petrol, diesel, paraffin
2.
Peat is not a common fuel because land has been cleared for building roads and houses.
3.
Liquefied hydrogen gas which is produced from the electrolysis of water is called gasohol.
4.
Using hydrogen as a fuel has one big advantage that when it burns the waste product is water.
5.
Hydrogen is a gas that catches fire easily.
Burning fuels: p 101
1.
2.
104
a)
Fuels that contain hydrogen and carbon are called hydrocarbons.
b)
When a hydrocarbon burns, it produces carbon dioxide gas and water along with heat energy.
a)
When a hydrocarbon burns in a plentiful supply of oxygen, carbon and hydrogen of the
hydrocarbon combine with oxygen to produce carbon dioxide and water (hydrogen oxide).
b)
Methane is a hydrocarbon having the formula CH4; when it burns in air CO2 + H2O and heat are
formed.
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3.
a)
In a limited supply of air, there isn’t enough oxygen to combine fully with carbon. Instead of
carbon dioxide a new compound called carbon monoxide is formed.
b)
When methane burns in a limited supply of air, carbon monoxide + water + heat energy is formed
along with soot (unburnt carbon).
4.
Carbon monoxide has no colour or smell so it is not easily detected. If it is breathed in, it prevents
the blood from carrying oxygen. It produces headaches and drowsiness in low concentrations. At high
concentrations it causes suffocation.
5.
In a car engine there is only a limited supply of air so the petrol never burns completely to form
carbon dioxide and water. Exhaust gases contain about 10% carbon monoxide. This is why an engine
should never be run in a poorly ventilated space such as a closed garage.
Chemical reactions as energy sources: p 102
1.
The more reactive a metal is the more likely it is to exist as a compound.
2.
a)
In a Thermite reaction a dry mixture of aluminium and iron(III)oxide is heated. The heat breaks
the chemical bonds holding the iron and oxygen together. Aluminium attracts the oxygen away
from the iron(III)oxide away and forms a new compound—aluminium oxide. Iron is left as a pure
substance.
b)
This is an exothermic reaction, so it is used to weld railway lines together.
3.
An exothermic reaction is a chemical reaction in which a lot of heat is given out.
4.
a)
The flow of electrons is electricity.
b)
The Voltaic or simple cell has two electrodes (plates), one copper and one zinc dipped in dilute
sulphuric acid (the electrolyte). The zinc slowly dissolves in the acid in the form of positive ions,
and electrons are left on the zinc plate. The copper does not dissolve. It loses electrons to positive
hydrogen ions in the acid, turning them into molecules of hydrogen gas.
Because of these chemical reactions, the zinc plate is left with too many electrons and becomes
negatively charged. The copper plate loses electrons and becomes positively charged.
When the two plates are connected to a bulb, electrons flow from the zinc round to the copper to try
and restore the balance. This flow of electrons is electricity.
New materials through chemistry and foodstuffs: p 103–104
1.
Synthetic means not occurring naturally.
2.
Glass reinforced plastic (GRP), Lycra.
3.
Lycra gives a tough fabric with a stretch, which keeps its shape well.
4.
Insulin is produced by a process called genetic modification. Scientists insert a gene into bacteria
which instructs them to make insulin.
5.
a)
flavourings, colourings, preservatives, and emulsifiers
b)
They are designed to make our food more appealing and last longer.
Conservation of mass (1): p 105
1.
By weighing materials before and after an experiment, Lavoisier discovered that the mass remained
the same during a chemical reaction.
2.
When a new substance is made during a chemical reaction, the number of atoms remains the same
but the way they are joined together changes. Mass is conserved.
3.
Some chemical reactions appear to lose mass because one of their products might be a gas which
escapes before we realize it.
4.
In the reaction between marble chips (calcium carbonate) and hydrochloric acid, the reaction appears
to have lost mass. But if we place a balloon over the flask, we will observe that there is no change in
mass as the gas that was produced has collected in the balloon, and there is no change in mass.
5.
Rate of a reaction means how fast the reaction is taking place. We could measure the volume of the
gas produced at regular time intervals, or we could weigh the apparatus at regular intervals.
Conservation of mass (2): p 106–107
1.
magnesium oxide
2.
To add oxygen.
3.
Start the experiment by heating gently. Lift the lid carefully.
4.
a)
0.4g
b)
1.66g
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5.
c)
4g
d)
40g
It seems that magnesium oxide weighs more than the magnesium in this experiment, but this is
because magnesium has combined with the oxygen of the air which we could not measure.
Test yourself: p 108
1
2.
3.
4.
5.
6.
a)
methane
b)
i)
carbon dioxide, water, and heat energy
ii)
carbon monoxide, water, unburned carbon, and heat energy
c)
LPG
d)
natural gas
a)
i)
B
b)
i)
It is an exothermic reaction.
ii)
From the graph of the reaction we can see that more heat energy is released at points B and
C as compared to the amount of energy that was put in point A to start the reaction. In other
words, the energy level of the reactants was more than that of the products.
ii) D
iii) C
iv) E
v) A
a)
i) carbon rod
b)
To keep the anode and cathode separate.
ii) zinc container
c)
i) powdered carbon
d)
To allow electrons to move freely.
e)
electrical energy
a)
A composite material is made up of two or more materials mixed together.
b)
It is used in places where light can pass through.
c)
It is resistant to corrosion so it is used in the construction of boats, surf boards, and some car
bodies.
d)
Plastics made with carbon fibres and denim combined with Lycra.
a)
Iron 1 atom, sulphur 1 atom.
b)
0.56g + 0.32g = 0.88g
c)
5.6g iron, 3.2g sulphur
d)
i) Yes
a)
1.6g
b)
i) water
c)
copper oxide + hydrogen ‡ copper + water
d)
The lesser the time that the copper oxide was heated for, the lesser the amount of copper
produced.
ii) to keep it dry
ii) The masses of iron and sulphur add up to the final mass of iron sulphide.
ii) it evaporates
Workbook 3, chapter 11
1.
a)
b
Fuel
Source
alcohol
product of fermentation of sugar
coal
mined from underground
liquefied hydrogen
made by electrolysis of water
oil
pumped from underground
paraffin
made from crude oil for heating and lighting
peat
cut from boggy land
petrol/diesel
made from crude oil as fuel for cars and lorries
i)
alcohol, liquefied hydrogen gas, peat
ii)
Alcohol is produced by the fermentation of sugar which is derived from the sugar cane
plant.
Liquefied hydrogen is produced from the electrolysis of water.
Peat is produced when plants and trees rot over millions of years.
2.
106
a)
The hydrogen atoms make a triangular pyramid. The carbon is at the centre of the pyramid.
b)
A hydrocarbon is a compound made up of the elements; carbon and hydrogen.
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3.
c)
CH4
d)
A fuel is something that is burnt to produce heat.
e)
carbon dioxide, water, and heat energy
f)
Carbon monoxide is a dangerous gas because it stops the oxygen from going into the blood. It
can make a person unconscious and even cause death.
g)
coal
a)
aluminium + iron(III)oxide ‡ aluminium oxide + iron
b)
Aluminium is higher up in the reactivity series.
c)
The Thermite reaction is a highly exothermic reaction.
d)
In the Thermite reaction, a dry mixture of aluminium and iron(III)oxide is heated. The reaction
is exothermic because the reactants react to reach a maximum temperature, at which the heat
energy breaks the chemical bonds holding the iron and oxygen together. The energy possessed
by the reactants is more than that of the products.
e)
4.
The simple cell has two electrodes, one copper and one zinc. The electrolyte is dilute sulphuric acid.
A series of chemical reactions takes place. The zinc plate is left with too many electrons and becomes
negatively (-) charged. The copper plate loses electrons and becomes positively charged.
When the two plates are connected in an electric circuit, electrons flow from zinc round to the copper
to try and restore the balance. The flow of electrons is electricity.
5.
6.
7.
a)
The material is called GRP because it is made by mixing glass fibres with a liquid plastic resin.
b)
1. composite fabrics
c)
It is made by mixing glass fibres with a liquid plastic resin.
d)
Lycra. It is combined with cotton fibres to make denim, which is used for making jeans.
a)
B
b)
A
c)
C
d)
i) A
ii) When heated in air, it gains mass and forms magnesium oxide.
e)
i) C
ii) It loses mass because it produces carbon dioxide gas when heated.
f)
i) B
ii) There is no change in mass by heating.
a)
Water evaporates and it forms a white powder.
b)
It turns blue again.
c)
i) When water is added.
d)
i) Yes
ii)
2. plastics to make racing car bodies
ii) When blue copper sulphate is heated.
There is no change in the mass of copper sulphate because when you add 0.9g of water to
1.59g of copper(II)sulphate to return it to its original state, the mass still equals 2.49g.
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Project
Making plastic
You will need:
Muslin cloth, jars, milk, vinegar, spoon, saucepan, elastic band, spirit lamp
Method
Warm about a cup of milk in a pan, but do not boil. Add a table spoon of vinegar and stir it.
A white rubbery material, the casein, forms in the milk. Strain it off through muslin held over a container.
Squeeze the milk through the muslin until you have recovered all the solid rubbery casein. Push the
material into a suitable mould, such as a pastry cutter, or shape it by hand. Then leave it to set.
Over a few days, the casein will gradually dry out and harden as the protein molecules bond tightly
together. If you wish to make a brooch, push a safety pin into the back while it is still soft. Once set,
paint it in your own design.
Multiple Choice Questions
1.
Which one of the following is not a fuel that comes from oil?
A petrol
2.
B diesel
4.
B CNG
6.
7.
9.
D GCN
NGC
A carbon dioxide, water, and heat
B carbon dioxide, oxygen, and heat
C carbon dioxide, water, and heat
D carbon dioxide, hydrogen, and heat
Which poisonous gas is produced by the incomplete combustion of methane?
B carbon dioxide
C chlorine
D phosgene
Which chemicals are heated in the Thermite reaction?
A aluminium and iron carbonate
B aluminium and iron oxide
C aluminium and iron sulphide
D aluminium and iron chloride
Which one of the following is not a composite material?
A glass reinforced plastic
B plastics
C Lycra
D paper
Which one of the following is not a natural composite material?
A wood
8.
C
The products of the complete combustion of methane are
A carbon monoxide
5.
D paraffin
Compressed natural gas is also known as
A CGN
3.
C coal
B glass
C bone
D ivory
What happens when a new substance is made during a chemical reaction?
A The number of atoms remains the same.
B The number of atoms increases.
C The number of atoms decreases.
D The number of atoms disappears.
The relative atomic masses of magnesium and oxygen are 24 and 16 respectively. What would the
ratio of their masses be in a molecule of magnesium oxide?
A 24:16
B 12:16
C 6:16
D 3:16
10. In an experiment to find the formula of magnesium oxide, magnesium is heated in a covered crucible.
Why is the crucible covered with a loose-fitting lid?
A To prevent air escaping from the crucible.
B To prevent magnesium carbonate forming.
C To prevent magnesium oxide escaping from the crucible.
D To prevent water vapour entering the crucible.
Answers
1.
C
6. D
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2. B
3. C
4. A
5. B
7.
8. A
9. A
10. C
B
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Pressure and
moments
Unit flow chart
Pressure in gases
Pressure in liquids
Hydraulic machines
Levers and moments
Balance and stability
Aims and learning objectives
•
To show the relationship between force, area, and pressure
•
To describe some effects and uses of gases under pressure
•
To use the particle model to explain why liquids cannot be compressed
•
To apply the concept of transmission of pressure to calculate resulting force
•
To use the principle of moments to perform simple calculations
•
To show how levers operate including the maintenance of balance in the human body
Background information
Which causes most damage to a wooden floor, a boot with a flat sole or a stiletto heel?
Believe it or not, the stiletto heel can ruin carpets and punch holes in floors. This is not just because of
the high downward force, but because the force is concentrated on such a small area it produces a high
pressure.
Pressure is the word used by scientists to describe how concentrated a force is.
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A heavy shoulder bag with narrow straps can hurt your shoulders. You can push a drawing pin into a
notice board, but with the same force you cannot push the flat end of a pencil into the board. There is
pressure acting on our bodies all the time, only we don’t usually notice it because our bodies are used to
it—and are built to withstand it.
Why does a swimmer feel pressure in his ears? If he went deeper into the water, how would this affect the
pressure? Why does blood have pressure?
Why can it sometimes be difficult to stop the bleeding if you cut yourself deeply? What is responsible for
this pressure?
Unit introduction
Additional activity 1
Explain the following in terms of pressure and area:
Pressure
Area
Walking on sand hurts less than walking on pebbles
A rubber washer is used when you want to tighten a
Bolt in woodwork
Heavy animals need thick legs
Studs on football shoes
Blade on a knife sharpener
Point on a drawing pin
Teaching procedure
Ask the students: what is pressure? How can we find out the pressure on the surface of a body?
Explain that pressure tells you how concentrated a force is. It is calculated using the equation: pressure =
force/area.
Pressure is measured in units called pascals (Pa). When 1N force acts on an area of 1 square metre we say
there is a pressure of 1 pascal.
Atmospheric pressure
Ask the students: does the air exert pressure? Can we feel it?
Explain that the Earth’s atmosphere contains billions of tonnes of air. At sea level, atmospheric pressure is
equivalent to a force of about 100,000 newtons pushing on every square metre.
Additional activity 2
Take an empty plastic bottle with a screw top. Make a hole close to its base. Put a finger on the hole
and fill the bottle with water and screw on the cap tightly. Remove your finger from the hole. Does
water come out of the hole in the bottle? Why? Now loosen the cap. What happens? Why?
Additional activity 3
Completely fill a glass with water. Hold a stiff card over the top of the glass and turn it upside down.
Then let go of the card. What happens? Can you explain why?
You can use your ideas about pressure to explain the above examples.
The atmosphere is a deep ocean of air which surrounds the Earth. In some ways it is like a liquid—its
pressure acts in all directions; its pressure feels less as you rise up through it.
However, unlike a liquid, air can be squashed. This makes the atmosphere much denser at lower
levels. The atmosphere stretches hundreds of kilometres into space, yet, most of the air lies within 10
kilometres of the Earth’s surface.
Down at sea level, atmospheric pressure is about 100,000 Pa. That’s equivalent to the weight of ten
cars pressing on every square metre.
You use your lungs to lower the air pressure in the straw when you suck a liquid out of a glass or a
bottle. Is it possible to suck the water out of a bottle which is tightly sealed? Why?
Pressure in gases
Ask the students: does a gas exert pressure? How?
Explain that in a gas the molecules are continuously moving, so at any time many of them are colliding
with the sides of the container. They bounce off without losing any energy, and in doing so each one
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exerts a small outward force on the wall. Because billions of molecules are doing this in each second, the
force appears as a constant pressure.
Additional activity 4
Fill a bicycle pump with air and place your finger over the hole at the bottom of the pump. Now press
the handle slowly. What happens? Now press the handle down still further. What happens? Release the
handle at this stage. What happens? If you keep pressing the air, you will get to a stage where your
finger is pushed away and some air escapes. Why do you think this happens? Feel the pump. Is it hot
or cold?
Explain that the pressure increases because the molecules have less space to move around in, so they
have more collisions with the walls of the container in each second.
Additional activity 5
Take a tin can with a tight-fitting push-on lid and put a small quantity of water in it. Heat the can over
a Bunsen burner till it fills up with steam. What happens? Explain your observation using the words
pressure, force, and temperature.
Explain using the kinetic theory what is happening to the water molecules throughout this activity.
Explain why it would be dangerous to do this experiment with water contained in a metal can with a
screw top?
Explain that as the gas is heated the molecules get energy, so they strike the walls with greater force.
They also have more collisions with the walls every second. These two factors make the pressure of the
gas increase.
Pressure in liquids
Ask the students: do liquids exert pressure?
Explain that liquids have two special features:
•
They cannot be squashed
•
If a trapped liquid is put under pressure, the pressure is transmitted to all parts of the liquid.
Discuss hydraulic machines which use liquid pressure to transmit forces from one place to another. Most
hydraulic machines are force magnifiers. They give out more force than is put in. This happens because
the output piston is larger than the input piston. To find out why, study the diagram on page 114. Like
all other machines, hydraulic machines cannot give out more work than is put in: work = force x distance
moved.
So, if a machine increases force it decreases the distance moved. In other words, the output force does
not move as far as the input force.
Additional activity 6
To investigate a simple hydraulic system.
Make a hydraulic cylinder using two syringes and a length of tubing. Join them as shown in the
diagram.
water
Move the plunger of one of these syringes in an out. What effect does this have on the other syringe?
Try using syringes of different diameters. See what effect this has.
What features do you think a hydraulic system should have if it is to be a distance magnifier; a force
multiplier?
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111
Additional activity 7
Decide whether each of the following statements is ‘true’ or ‘false’.
1. Liquids are virtually impossible to compress.
2. If a trapped liquid is under pressure, the pressure is transmitted throughout the liquid.
3. A machine can give out more work than is put into it.
Machines
Ask the students: what is a machine? What can a machine do?
Explain that anything which makes forces more convenient to use is called a machine. It may be as
complicated as a gear box or as simple as a pair of scissors. Discuss the effects of machines.
Some machines are force magnifiers. A pair of pliers, for example, gives you greater force at the jaws
than you put into it at the handles
Some machines are movement magnifiers. A bicycle for example, one downward push on the pedals takes
you forward over 3 metres—much further than one step would take you if you were walking.
Additional activity 8
Make a list of machines which are:
Force magnifiers
Movement magnifiers
1. Nail clippers
Hand drill
2.
3.
4.
5.
Levers and moments
Ask the students: what is a lever? What can a lever do? Is a lever a machine?
Explain that kitchen scales balance when the weights on each side are the same. If there is more weight in
the left-hand pan then that side moves down. This is because the larger force has a bigger turning effect
about the movable point, the pivot.
Explain that the turning effect of a force is called its moment.
Ask the students: what do you think the moment of a force depends on?
Explain that the moment of a force depends on how big the force is. It also depends on the distance of
the force from the pivot or fulcrum.
The diagram on p 115 of the student’s book shows how a large force can be balanced by a smaller force.
Notice that the smaller force is further away from the pivot. This increases the turning effect.
1m
0.5m
50N
100N
�������������������������������� ���� �� ��� �� ����
��������������������������������� ����� �� ����� �� ����
112
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Using moments
Ask the students: how are levers useful?
Discuss that people have known how to use the moment of a force to do work for thousands of years. For
example, the Egyptians used levers and other simple machines to move heavy blocks of stone to make the
pyramids about 50,000 years ago.
Useful levers
Show by practical activity how levers are useful.
A small effort applied to the end of a hammer can overcome the force holding the nail in the wood.
A long-handled spanner allows a small effort to overcome large forces holding the nut on.
Balance
Ask the students: how are objects balanced?
Explain that a metre rule will balance if it is supported at its mid-point. This is because the weights of all
the particles on one side of the pivot are balanced by the weights of all the particles on the other side. It
appears as though all the weight is acting at one point. This point is called the ‘centre of gravity’.
Additional activity 9
Show the students different shaped objects such as a ball, a cone, a funnel, a metre rule, etc. Ask
them to balance them at their centre of gravity.
Explain that for uniform objects like metre rules and billiard balls, the centre of gravity is where you
would expect—right in the centre. For other shapes you may have to carry out a simple investigation to
find out.
Additional activity 10
Cut a shape out of a thick piece of card. Punch holes near two corners. Now hang the card from a nail
or pin as shown in the diagram
pin
centre of gravity
plumb line
Use a plumb line to mark a vertical line.
Repeat this with the card suspended from the other corner. Where the two lines cross is the centre of
gravity.
Stability
Ask the students: what will happen to a cone if we try to balance it on its pointed end?
Explain that some things fall over easily when pushed. Others are difficult to topple. We say that these
are stable. As long as the centre of gravity stays above the base of an object it won’t topple over. A heavy
truck is in stable equilibrium. If it starts to tip, its weight will pull it back again. A racing car is even more
stable than the truck. It has a lower centre of gravity and a wider base. It could be tipped much further
before it started to topple.
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Equilibrium
Stable equilibrium
Even if you tip the cone a little, the centre of gravity stays over the base.
equilibrium
equilibrium
equilibrium
centre of gravity
centre of gravity
centre of gravity
Unstable equilibrium
This cone is balanced but not for long. Its pointed base is so small that the centre of gravity immediately
passes beyond it.
Neutral equilibrium
Left alone, the ball stays where it is. Moved, it stays in its new position. Wherever the ball lies, the centre
of gravity is always exactly over the point where it touches the bench.
Additional activity 11
kitchen stool about
to topple over
The kitchen stool is about to topple. Mark the position of the centre of gravity of the stool.
Would the stool be MORE stable or LESS stable, if it had:
a) a higher centre of gravity
b) a wider base?
Explain why a three-legged stool is not as stable as a stool with four legs.
114
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Answers
Pressure and moments: p 110–111
1.
Pressure is the result of a force acting on a certain area.
2.
The blunt end.
3.
a)
Surface area is indirectly proportional to pressure, the greater the surface area the lesser the
pressure.
b)
Force is directly proportional to pressure, the greater the force the greater the pressure.
4.
Force is indirectly proportional to pressure. This means that a large surface area will produce less
pressure. A pointed pin with a small surface area will produce greater pressure.
5.
a)
P = F/A
P = 550N/1= 550Pa
b)
P = 550N/10
c)
A flat heel will produce less pressure because it has a greater surface area. This is because force
is indirectly proportional to area—the greater the area the lesser the pressure.
= 55Pa
Pressure in gases: p 112
1.
The molecules are far apart, so air can be squashed.
2.
Compressing a gas heats it up because the molecules move faster.
3.
If the volume of a gas is halved, the pressure is doubled.
4.
The switch on the spa bath is pneumatically controlled. Air is compressed in the tube by a push button
which, in turn, operates the switch on the electric motor which drives the pump.
5.
Pneumatics help to make spa baths safe to use because the switch of the bath pump is pneumatically
controlled. The compressed air in the tube acts as an insulator.
Pressure in liquids: p 113
1.
The weight of the liquid pushes down on the base creating a pressure.
2.
Dense liquids have a greater weight for the same volume so they press down on the container with
greater pressure.
3.
If you observe the level of tea in a teapot, it is at the same level as the tea in the spout. Adding more
water to the pot causes the tea to rise to the same level in each section. This shows that the pressures
in the pot and the spout are the same.
4.
Submarines need thick, strong walls because the water exerts a pressure on its body which may cause
it to collapse. This pressure is called hydrostatic pressure.
5.
a)
Pressure
=
Force
Area
=
4500
=
3000Pa
=
4000Pa
1.5
b)
6000
1.5
Hydraulic machines: p 114
1.
Liquids are very difficult to compress because their particles are very close together.
2.
An input cylinder is narrow while an output cylinder is wider.
3.
They have thick walls because they have to bear a lot of pressure exerted by the hydraulic system.
4.
Pressure exerted on the narrow cylinder is transmitted by the oil to the wide piston. It produces an
output force which is larger than the input force. The jack acts as a force multiplier.
5.
Compressing the gas heats it up causing its molecules to move faster. This increases the pressure.
It can cause an explosion.
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115
6.
Pressure on narrow syringe (P) = F1/A1
= 6/2
= 3Pa
Force at wider end (F2)
= P x A2
=3x8
= 24N
Levers and moments: p 115
1.
A lever is a simple machine. It helps to make work easier.
2.
a)
Effort is the force that is applied to the end of a long lever.
b)
Load is the force to overcome by a machine.
c)
Pivot is the point of rotation of a lever.
3.
A turning effect of a force is called a moment.
4.
Clockwise moment is the turning effect of a force in a clockwise (towards the right) direction.
Anticlockwise moment is the turning effect of a force in an anticlockwise (towards the left)
direction.
Moments in balance: p 116
1.
2.
a)
Fred should sit at a distance of 4 metres.
b)
Jill is sitting in the right place i.e., at 3 metres from the pivot.
I would hang the bag of cement at one end of the wooden plank and make my friend sit at the other
end and make my friend move backwards and forwards till the clockwise and anticlockwise moments
were equal. Then I would calculate the moments on both sides:
Weight of bag x distance from pivot = weight of friend x distance from the pivot
3.
a)
The size of the force on each side and the distance between each force and the pivot.
b)
The sum of the clockwise moments equals the sum of the anticlockwise moments. This is called
equilibrium.
Balance and stability: p 117
1.
Muscles move bones at joints so that individual bones can act as levers.
2.
a)
At joints, muscles are arranged in pairs so that one muscle of the pair pulls the joint one way
and the other pulls it back again. Because the muscles work against each other, they are called
F = 600N
antagonistic pairs.
b)
They help in body movements.
a)
When the biceps contract, it helps to flex or bend the arm.
3.
b)
4.
5.
When the triceps contract, it helps to straighten the arm.
4cmit is unstable. When something is difficult to topple
When something falls over easily when pushed,
it is stable.
The stability of an object depends on how far it can be tipped before its weight moves outside its
base. When this happens the moment of the weight tips it over.
Test yourself: p 118–119
1.
2cm
3cm
a)
i)
ii)
F = 600N
F = 600N
4cm
2cm
2cm
3cm
116
= 600N
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3cm
4cm
b)
P
=
F/A
=
600/ (3 x 2)
=
600N
=
6cm2
P
=
600/0.0006
=
1 000 000Pa
=
F/A
=
600/ (4 x 3)
=
600N
=
12cm2
2.
a)
=
600/0.12
=
500000Pa
P
=
F/A
F
=
A =
P
3.
4.
600N
0.0006m2
600N
0.0012m2
600N
200 x 4cm2
=
800cm2
=
0.08m2
=
600/0.08 = 7500Pa
b)
The camel’s wide feet prevent it from getting trapped in the sand.
a)
The pressure of the fluid in the system would be directly proportional to the force applied and
inversely proportional to the area of the narrower syringe.
b)
A smaller force is required.
c)
The output force would be greater.
d)
This principle is used in disc brakes of motor cars and motorcycles.
a)
i)
X
ii)
Moment of X is equal to force applied 20N multiplied by the distance from the pivot
0.3m = 6Nm
Moment of Y is 40N x 0.2cm = 40N x 0.002m = 0.08Nm
5.
6.
b)
By applying the force at the end of the spanner Y instead of at the centre.
c)
The turning effect is called torque.
a)
The moment at the left-hand side is 20Nm and the moment at the right-hand side is 12Nm. These
forces are not balanced.
b)
By adding a force of 2N to the right-hand side we could balance the plank.
a)
Traffic cones have stable equilibrium.
b)
Bowling pins have an unstable equilibrium.
c)
Passengers standing on the upper deck have unstable equilibrium.
d)
The stability of an object depends on how far it can be tipped before its weight moves outside
its base. Objects with wide bases and a low centre of gravity (centre of mass) are more stable. A
half empty bottle is more stable than a full one because its centre of gravity is lower than that
of a full bottle. Therefore we say that the half-empty bottle is in stable equilibrium.
Workbook 3, chapter 12
1.
a)
Pressure is indirectly proportional to area. Stiletto heels have a very pointed base which has a
small area as compared to the weight of the person wearing it.
b)
Snow shoes have a wide base so they will have lesser pressure as compared to shoes with narrow
bases.
c)
Football shoes have studs which have a narrow area to give the players a better grip on the ground
when they are running.
d)
A bed of nails has a wider area than a single pin, so the pressure of the bed of nails will not hurt
him.
e)
The handles of the heavy bags have a narrow area as compared to the force of the things inside
so the pressure is greater.
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2.
f)
The area of the camel’s feet produces less pressure as area is indirectly proportional to pressure,
so a camel can easily walk on the sand without getting stuck.
a)
P = FxA
= 120N x 0.01m = 1.2Pa
b)
P = FxA
c)
It has an unstable equilibrium when it is made to stand at its pointed end.
a)
50 x 0.002 = 0.01Pa
b)
2 500 000N
c)
250 000N
d)
A
a)
i)
spanner 2
ii)
The force is applied at a longer distance so less effort is needed to turn the nut.
= 120N x 0.001 = 0.12Pa
3.
4.
b)
spanner 1:
moment
= force x weight of the arm
= 10N x 0.2m = 2Nm
spanner 2:
moment
= force x weight arm
= 10N x 0.4m = 4Nm
c)
torque
d)
A small effort applied at the handle of the spoon overcomes the force holding the lid in the tin.
This is similar to the working of a spanner where the long handle of the spanner allows a small
effort to overcome the large force holding the nut on.
length of spoon
lid
force
tin
5.
turning point
See-saw 1
a)
i)
900Nm
b)
unbalanced
ii)
600Nm
ii)
600Nm
ii)
600Nm
See-saw 2
a)
i) 300Nm
b)
unbalanced
See-saw 3
6.
118
a)
i) 600Nm
b)
balanced
Levers, shorter, relax, push, antagonistic, forearm, biceps, triceps.
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7.
The beaker has a stable equilibrium. It has a wide base.
The test tube has an unstable equilibrium. It has a narrow base.
The cylinder has a stable equilibrium. It has a wide base.
The filter funnel has an unstable equilibrium. It has a narrow base.
The conical flask has a stable equilibrium. It has a wide base.
Project
Perching parrot
You can make this balancing toy to exploit the natural stability of objects with a low centre of gravity.
You will need a piece of stiff cardboard, some coloured pencils or paints, a pair of scissors, a wooden
ruler.
Trace the outline of the parrot, transfer it to stiff cardboard and cut it out. Pin it to a wooden ruler.
Because the centre of gravity is actually directly below the pivot point, the parrot swings back upright
even when it is tipped over some way.
Multiple Choice Questions
1.
In which of the following examples is the greatest pressure exerted?
A A barefooted person standing on the beach.
B A brick resting on the ground.
C A knife cutting a piece of meat.
D An elephant standing on the ground.
2.
A tank is 3m long, 1m wide and 0.5m deep is filled with oil which weighs 12,000N. What is the
pressure on the base of the tank due to the oil?
A 4000Pa
3.
B 6000Pa
C 8000Pa
D 10 000Pa
A spanner is used to loosen a nut. The turning effect depends on the force applied and the
perpendicular distance from the force to the nut. Which name is given to the turning effect?
A moment
B pivot
C pressure
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119
4.
5.
If a nut and a bolt are difficult to undo, it may be easier to turn the nut by using a longer spanner.
This is because a longer spanner gives
A a larger turning moment
B a smaller turning moment
C less friction
D more friction
Some gas trapped in a cylinder is compressed at constant temperature by a piston. Which of the
following will not change?
A density
6.
7.
B mass
C pressure
D volume
When the temperature of a gas rises at constant volume, its molecules
A move closer together
B with greater average speed
C collide with on another less often
D expand
Which one of the following statements is not true for pressure in liquids?
A Pressure pushes in all directions.
B Pressure increases with depth.
C Pressure is affected by the density of the liquid.
D Pressure is affected by the width and shape of the container.
8.
The way your forearm moves is similar to
A pulley systems
B inclined planes
C levers
D a spring balance
9.
���
����
����
����
What is the distance of (d)?
A 10cm
B 20cm
C 30cm
10. Which one of the following is the most stable?
A An object with a narrow base and low centre of gravity.
B An object with a wide base and low centre of gravity.
C An object with a narrow base and high centre of gravity.
D An object with a wide base and high centre of gravity.
Answers
1.
C
6. B
120
2. A
3. A
4. A
5. B
7.
8. C
9. B
10. B
D
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1 period
40 mins.
1 period
40 mins.
1 period
40 mins.
1 period
40 mins.
Time
Objectives
To know the names of
some salts and describe
some uses for them.
To learn that when an
acid reacts with an alkali,
a neutralization reaction
occurs and salt and water
are formed.
To learn that different
acids react in a similar way
with metals, their oxides
and their carbonates.
To list the properties of
metals.
Write the properties of metals and non-metals.
Write the chemical equations for the following reactions:
acid + metal
acid + metals carbonate
acid + metal oxide
acid + alkali
Write the names and chemical formula of five salts used as
fertilizers.
1
2
3
Assessment Tasks
Neutralization
reactions
3
Some common salts
and their uses
Reaction of metals
with acids and reaction
of acids with metals
oxides, carbonates,
alkalis
2
4
Properties of metals
1
Topic
Outcomes
An electrolytic
cell, sodium
chloride
solution.
Test tube to
collect chlorine
gas
Pipette, burette,
conical flask,
acid and base
solutions
indicator
Chemicals,
beakers,
funnels, filter
paper, stirrers,
china dish,
Bunsen burner
Samples of
different metals
Chart of the
particle model
Resources
Needed
Teacher’s evaluation of the lesson
Background information (5 mins.).
Introduction (5 mins.).
Practical demonstration of
electrolysis of Sodium Chloride
solution (20 mins.).
Discuss chemical fertilizers and
their use (10 mins.).
Background information (5 mins.).
Introduction (5 mins.).
Practical demonstration (20 mins.).
Discussion and assessment (10
mins.).
Background information (5 mins.).
Introduction (5 mins.).
Practical demonstration (20 mins.).
Discussion and assessment tasks
(10 mins.).
Background information (10 mins.).
Introduction (10 mins.).
Practical demonstration (10 mins.).
Discussion on properties of metals
(10 mins.).
Plan (Activities) Time
Write the answers to all the questions on
p 10 to p 19.
Homework
To know how electolysis
is used to obtain useful
substances from salts.
To know the importance of
some useful salts that are used
as fertilizers.
To know how and why a
titration is carried out.
To understand the use of
indicators.
To identify the end products of
a neutralization reaction.
To identify patterns in these
reactions and produce general
equations.
To identify evidence which
indicates a chemical reaction
has taken place.
To represent the reactions in
word and symbol equations.
To use the particle model
to explain the properties of
metals.
Sample lesson plan: Unit 2 Reaction of metals
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Explain how a skater can slide along the ice.
How can you explain the behaviour of gases by the particle model?
What properties of liquids help hydraulic machines to operate?
What is equilibrium?
What does the stability of an object depend on?
1
2
3
4
5
To show how levers
operate including the
maintenance of balance in
the human body.
Assessment Tasks
1 period
40 mins.
Levers and moments
To compare pressure
in gases with pressure
in liquids, and to give
examples of their uses.
To understand and use the
relationship between force,
area and pressure.
3
1 period
40 mins.
1 period
40 mins.
Objectives
Pressure in liquids
Pressure in gases
Time
2
1
Topic
A metre-rule,
thread, weights,
different kinds
of objects used
as levers, charts
showing bones
as levers
Objects to
show stable
and unstable
equilibrium
Containers
of different
shapes, beakers,
container
with holes at
different depths,
syringes, rubber
tube
Objects with
varied surface
areas.
A wooden
rectangular
block
Resources
Needed
Teacher’s evaluation of the lesson
Background information (5 mins.).
Introduction (5 mins.).
Practical demonstrations of
moments in balance and levers
(20 mins.).
Discussion and assessments tasks
(10 mins.).
Background information (5 mins.).
Introduction (5 mins.).
Practical demonstration (20 mins.).
Discussion and assessment tasks
(10 mins.).
Background information (5 mins.).
Introduction (5 mins.).
Practical activity (10 mins.).
Calculating pressure (10 mins.).
Discussion and assessment (10
mins.).
Plan (Activities) Time
Attempt all the questions on p 111 to p 119.
Homework
To explain the action of levers,
and to use the principle of
moments to perform simple
calculations.
To understand the relation
between balance and stability.
To use the particle model to
explain why liquids cannot be
compressed.
To apply the concept of
transmission of pressure to
calculate the resulting force.
To describe some effects and
uses of gases under pressure.
To use the particle model to
explain the behaviour of gases.
Outcomes
Sample lesson plan: Unit 12 Pressure and moments
Test Paper 1 (Units 1 to 4)
Total marks: 100
Section 1
[total marks 40]
A Fill in the blanks to complete the statements.
1. Human cells have
[marks 10]
chromosomes in every body cell.
2. The joining up of the sperm and egg is called
3. Metals can conduct heat and
4.
.
.
gas is produced by the reaction of an acid and a metal.
5. Ammonium nitrate is a salt which is useful
.
6. The driving force of a current is called
7. All materials have a
.
to the flow of electricity through them.
8. A
contains a thin piece of wire which will melt if the
current gets too high.
9.
power stations convert energy from fuel into electrical
energy.
10.
B
are substances that change the way a body works.
Match the items of list A and B
A
[marks 10]
B
1. Chromosomes and genes
can conduct electricity
2. Male gametes are called
can be hammered into shape
3. GMOs are
the concentration of a solution
4. Graphite is a non-metal that
25g of sodium chloride per litre
5. Malleable means
created nor destroyed
6. Titrations help to find
are made of DNA
7. The sea contains about
sperms
8. Energy can neither be
genetically modified organisms
9. Voltage is measured by
the same resistance
10. A perfect resistor always has voltmeter
C State whether the statements are ‘True’ or ‘False’.
[marks 10]
1. Sex cells are called homologous chromosomes.
2. Clones are genetically identical organisms.
3. Metals have densities and low melting points.
4. When metals react with acids, carbon dioxide gas is produced.
5. When an alkali and an acid react together a salt and water are formed.
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6. The percentage of energy supplied to a device which is usefully
transferred is called its efficiency.
7. Voltage is usually measured in ohms.
8. Current is directly proportional to the voltage.
9. Fibre is made up of animal cell walls which pass through the digestive
system without being digested or absorbed.
10. Caffeine is a mild stimulant found in tea and coffee.
D Choose the best answer.
[marks 10]
1. Which one of the following is not a harmful drug?
A heroin
B cannabis
C aspirin
D LSD
2. Which one of the following is a protein deficiency disease?
A scurvy
B kwashriorkor
C rickets
D night blindness
3. Fats and sugars are foods that
A provide energy
B provide building materials
C control chemical reactions
D contain fibre
4. How much energy in fuel is converted into electrical energy?
A 15%
B 25%
C 35%
D 45%
5. One kilogram of uranium can produce as much energy as
of coal.
A 40
B 60
C 80
tonnes
D 100
6. Fuses and switches are always connected in the
A neutral wire
B live wire
7. A salt gets its name from the
A alkali
B acid
8. Non-metals do not have a sea of
conduct electricity.
A protons
B neutrons
C fuse wire
D switch wire
used in the reaction.
C water
D metal
in their structure so they do not
C electrons
D atoms
9. The reflecting surface of a mirror is a thin layer of which metal?
A silver
B gold
C mercury
D zinc
10. A person who has two identical gene alleles for a characteristic is called
for that characteristic.
A dominant
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B recessive
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T EACHER ’ S G UIDE 3
C homozygous
D heterozygous
Section 2
[total marks 10]
1. Look at the following diagram of cell division. Label the stages using the
words from the box below:
splitting up of chromosomes
new cells
replication of chromosomes
2. The following diagram shows the electrolysis of sodium chloride solution.
Label the diagram using the words from the box below.
chlorine
electrolysis tank
hydrogen
sodium chloride + water
sodium hydroxide
power supply
3. Diagram shows a hydroelectric power station. Label the diagram using the
words from the box below:
water running through pipeline
generator
turbines turnning
power station
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Section 3
[total marks 20]
Define the following terms:
Clone:
Ductile:
Efficiency:
Voltage:
Hallucinogens:
Section 4
[total marks 30]
Answer any 3 questions [all questions carry equal marks]
1. Write an essay on selective breeding in animals and plants.
2. Write an essay on understanding the properties of metals.
3. Write an essay on safety and electricity.
4. Write an essay on useful and harmful drugs.
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Test Paper 2 Units 9 to 12
[Total marks 100]
Section 1
[total marks 40]
A Fill in the blanks to complete the statements.
1.
[marks 10]
tells us how fast a thing is moving.
2. A body will not move if there is no
3. An object is
acting on it.
if its speed is changing.
4. Farmers add mineral elements to their soils in the form of
.
5. Plants make energy available to other organisms by trapping it from
.
6.
are used to kill any fungal competitors that might affect
food crops.
7. Fuels release
energy when they burn.
8. In a limited supply of air incomplete
takes place.
9. If a gas is squashed into a smaller volume, its
rises.
10. Materials which do not occur naturally are called
B
.
Match the items of list A and B
A
[marks 10]
B
1. Speed
rate of change of velocity
2. Acceleration
the pull of the Earth
3. Gravity
how fast a thing is moving
4. Mineral deficiency
an insecticide to grow more crops
5. Competition
not getting enough minerals
6. Eutrophication
heat energy from a displacement reaction
7. DDT
electrical energy from chemical energy
8. Thermite reaction
force acting on a certain area
9. Voltaic cell
all pond life dies due to this
10. Pressure
competing for similar things
C Write ‘True’ or ‘False’ against the following statements.
[marks 10]
1. Kilometres per hour is a useful unit for measuring speed.
2. The area under a speed-time graph is equal to the speed of the vehicle.
3. Sewage contains an excellent source of food for bacteria.
4. Many insects developed a resistance to DDT within 2 years.
5. Burning is a chemical reaction.
6. GRP is a plastic which is very tough and very heavy.
7. Most modern medicines are synthetic.
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8. Wood is an artificial composite material.
9. Dense liquids have a greater weight for the same volume.
10. Muscles which work against each other are called extensor muscles.
D Circle the correct answer.
[marks 10]
1. Things which fall over easily when pushed are
Stable
Unstable
2. The arm is extended by
Triceps muscle
Biceps muscle
3. The turning effect of a force is called
Moment
Momentum
4. Compressing a gas increases its
Volume
Pressure
5. During a chemical reaction mass is
Dispersed
Conserved
6. A chemical reaction in which heat energy comes is called
Endothermic
Exothermic
7. In the complete combustion of methane, the gas produced is
Carbon dioxide
Carbon monoxide
8. NPK is a
Natural fertilizer
Artificial fertilizer
9. Air resistance is a
Frictional force
Gravitational force
10. Retardation means that the speed of a car is getting
Less
More
Section 2
[marks 15]
1. Look at the following diagram of a parachutist free falling. Label the two
forces acting on his body.
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2. Look at the following diagram of a dry cell. Label the diagram using the
words from the box below:
carbon rod
contact
zinc container
(+) contact
insulating seal (–)
powdered carbon
Label the following diagrams:
i)
All three diagrams of sky diver p 87 (ii) Lever p 115
iii) A dry battery cell p 108 Q 3
Section 3
[marks 15]
1. Draw a labelled diagram to show the Eutrophication of a pond.
2. Draw a simple Voltaic cell and label it.
3. Draw a speed-time graph using the following information:
Time in seconds
0
1
2
3
4
5
Speed in m/s
0
4
8
12
16
20
Section 4
[total marks 30]
Answer any three questions [all questions carry equal marks]
1. What is the relation between gravity, falling and air resistance?
2. Why do farmers use fertilizers for growing crops?
3. How can you prove the law of conservation of mass experimentally?
4. Which properties of liquids do hydraulic machines use? How do they work?
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