PS548
SCIENCE FOR PRIMARY TEACHERS
TheOpen
University
LEARNING AND TEACHING CHEMISTRY
THROUGH TOPIC WORK
STUDY GUIDE
FUELS
1 lntroduction
2 What is a fuel?
3 The process of combustion
Activity 1 : Demonstrating the process
of combustion
4 A variety of fuels
5 Conclusion
MATERIALS
1 lntroduction
2 Materials-what kinds are there?
Activity 1 : What is a material?
Activity 2: Materials display
3 Using materials to develop process
skills
Activity 3: Making, recording and
discussing observations
Activity 4: Analysing observations
Activity 5: Raising questions for
investigation
Activity 6 : Isolating and controlling
variables
Activity 7: Designing a fair test
Activity 8: Identifying process skills
.4 Classifying materials: description and
properties
Activity 9: Classifying materials
Activity 10: Characteristics of metals
5 Developing children's ideas about
Activity 1 1 : Materials in use around the
school
Activity 12: Finding out what materials
are like
Activity 13: Finding out how materials
canbechanged
6 Conclusion
CLEAN SCIENCE
1 lntroduction
2 Shower gel manufacture
Activity 1: Assessing the competition
Activity 2: Design of gel containers
Activity 3: Measuring shower gel
viscosity
Activity 4: Manufacture of a shower
gel
Activity 5: Finalizing the product
Activity 6 : Marketing the product
Activity 7: Evaluation
3 The history of soaps and detergents
Activity 8: Keeping clean
Activity 9: Everyday dirt
4 The chemistry of soaps and
detergents
Activity 10: What can detergents do?
5 The way forward
RESOURCES
ACKNOWLEDGEMENTS
NOTES
materials
CENTRE FOR SCIENCE EDUCATION
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
STUDY GUIDE
We are all aware that teaching must be made more relevant to society to better
motivate our children and to give adults an informed opinion on scientific and
technological issues. During your study of Science for Primary Teachers you
may, at times, have found it challenging to relate some of the material to your
own professional needs. This part of the chemistry materials helps you to address
these needs.
The three topics included here draw on different areas of chemistry. They aim to
relate the chemistry you have considered to areas ,that are of concern or interest to
us as individuals and consumers.
The first topic, 'Fuels', mainly focuses on providing further information for
you, the teacher, and concentrates on aspects of fossil fuels as sources of energy.
Problems of pollution-a result of using these fuels-are also considered.
'Materials' is the second topic considered. Here, we start from children's ideas
and follow two main themes-classification and change. The importance of
developing and learning concepts through practical activity is addressed.
Finally, the chemistry of soaps and detergents is dealt with through the topic
'Clean science'. This material was developed in collaboration with Unilever
Research, Port Sunlight Laboratory. Here, you will mimic the research procedure
used in the development of a commercial shower gel. Although you may not
wish your children to do this particular activity, it will provide you with many
ideas that will be of use in the classroom.
For all three topics you will need to get together the equipment, materials and
chemicals that are listed in the 'Introduction to the Study Commentaries'. You
should do this before starting work on each topic.
In the work that you have so far completed we have emphasized not only the
scientific concepts but the context that you can use them in. We hope these three
topics help you to achieve that aim for chemistry and enable you to use some of
the knowledge gained.
SCIENCE FOR PRIMARY TEACHERS
FUELS
1 INTRODUCTION
Every day people use fuels in thousands of different ways-for example, to warm
houses, cook meals and light the streets. Fuels provide us with e n e r g y .
Although much of this energy is used in our homes, just as much is needed for
industry. We know that energy is vital to life, and questions such as 'What is
energy?', 'What do we use?', 'What do we need?', 'How much do we pay for it?'
are considered in Unit 9 of S102 and the associated Study Commentary.
We will look here at fuels as sources of energy, at how they provide us with that
energy and at the environmental problems that result from using them. Fuels
such as coal, oil and natural gas are called fossil fuels; they provide concentrated
sources of energy. In this part of the chemistry materials we will address only
the subject of fossil fuels; where we refer in the following discussion to a 'fuel',
therefore, it is implicit that we are talking about a fossil fuel. You will find a
discussion of nuclear fuels in 'Nuclear issues'.
As you work through the topic, take time to consider in which areas of the
primary curriculum you might include work on fuels, and the methods and
activities you could employ to translate the material given here into a suitable
form for key stages 1 and 2 of the national curriculum.
2 WHAT IS A FUEL?
Before considering a number of different fuels we need to be clear what we mean
by the term fuel.
Spend a minute or two jotting down some examples of fuels in Table 1. You
should be able to think of several different sorts. Try also to give an example of
what use might be made of each fuel that you list.
TABLE 1 Some examples of fuels and their uses
Fuel
Use
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
Your suggestions probably included gas (for heating and cooking), petrol (for
cars) and coal or coke (for heating or the production of electricity). Other wellknown fuels include oil and related substances, such as paraffin or kerosene, but
you might also have included materials such as wood, peat, straw or even cow
dung, which can all be burnt to provide heat.
0 Can you identify the essential property of a substance that makes it possible
to use it as a fuel?
'
Fuels undergo combustion, releasing energy, usually in thl form of heat
energy.
Thus a definition of a fuel would need to include this feature. The Concise
Oxford Science Dictionary defines a fuel as: 'A substance that is oxidized or
otherwise changed in a furnace or heat engine to release useful heat or energy.'
,
When you studied Unit 9 of S102 and the associated Study Commentary you
came across a number of different forms of energy. Here we are going to consider
the production of energy from various fossil fuels.
3 THE PROCESS OF COMBUSTION
The process of combustion is the burning of a substance in air or in oxygen. It
usually results in the liberation of heat energy to the surroundings. Often light
energy is also liberated, in the form of a visible flame. If this energy can be
gathered in some way and transmitted, it can provide power. For example, in an
oil-fired power station, oil (the fuel) is burnt to provide heat energy, which is
used to heat and vaporize water, turning it into steam. The steam is used to
provide mechanical energy to drive turbines, which produce electrical energy.
Activity 1 shows how you can demonstrate the process of combustion.
-
ACTIVITY 1 : DEMONSTRATING THE PROCESS
OF COMBUSTION
You will need:
small floating candle or night-light
small foil dish, such as an individual fruit-pie dish
container of water
large jam-jar
matches
If using a night-light, put it in a small foil dish that will float. Float the
candle or night-light in its dish on some water and have ready a jam-jar that
is large enough to cover it, so that the candle can bum in the air enclosed by
the jar.
Set up the equipment, but do not light the candle.
Place the jam-jar over the candle and lower the jam-jar into the water. Notice
what happens to the candle. (Note: You will be able to see the candle float if
the neck of the jam-jar does not touch the bottom of the container.)
Remove the jam-jar, light the candle and put the jam-jar back over it
immediately.
Allow the candle to continue to bum and note down what happens.
You should have seen the candle flame flicker and go out, and the water level
inside the jam-jar rise.
SCIENCE FOR PRIMARY TEACHERS
Wait for a minute or two after the candle has gone out until the water level
inside the jam-jar is steady. Now try to answer the following questions:
Cl
Why did the candle go out?
W
The candle burnt because the air available in the jam-jar contained
oxygen. When this oxygen supply had all been used up in the process
of combustion, the candle could burn no longer and so went out.
Cl
Do you think that any new substances were produced during the
burning? What might they be?
W
The main products of the combustion of a candle, which is mostly
composed of a hydrocarbon, would be carbon dioxide, water and soot
(carbon).
When paraffin burns in a paraffin heater the same thing happens-xygen
is
used up and carbon dioxide and water are produced. This is why considerable
extra ventilation is needed in a room heated by paraffin-to provide fresh air
for breathing and to reduce the amount of condensation.
Cl
Why did the water level rise inside the jam-jar?
W
During combustion, the volume of carbon dioxide produced is less than
the volume of oxygen used up. As a result, atmospheric pressure on the
water outside the jar is greater than the pressure on the water inside the
jar, so the water level inside rises until the pressures are equal again.
(The small volume of water produced by the combustion process would
have a negligible effect on the water level in the jar.)
Cl
Why was it necessary to wait for a minute or two after the experiment
to allow the water level to stabilize?
The air remaining in the jam-jar had been heated by the candle flame.
Since gases expand when heated and contract when cooled it was
important to wait until the gases remaining in the jam-jar had cooled
down again to room temperature and contracted. You can then be sure
that you are seeing the full effect of combustion on the level of water in
the jam-jar.
You could try doing the experiment again and measuring the time it takes for
the candle to go out from the moment when the air available to it is enclosed
by the jam-jar. Then you could investigate what happens if you use more
than one candle burning simultaneously inside the jam-jar. Do you think it
will take more or less time for the candles to go out? How long does it take
for each candle to go out? Is there a link with the time taken for one candle to
go out? Alternatively, you could repeat the experiment but this time vary the
size of jam-jar and hence the amount of air available to the candle. Investigate
the effect of this on how long the candle burns.
PRODUCTS OF COMBUSTION
What substances are produced during combustion depends on what the original
substance was, and whether or not there was enough air or oxygen present to
allow complete combustion. For instance, coal contains the element sulphur in
addition to carbon, so that when coal is burnt some compounds of sulphur and
oxygen are produced as well as compounds of carbon and oxygen. As you saw in
'Chemical reactions and energy changes', the presence of oxides of sulphur in the
air is a contributory factor to acid rain. (There are short discussions of acid rain
in Section 6.3 of Unit 15 of S 102, and in 'Introducing chemistry concepts'.)
The main product formed when carbon is burnt is carbon dioxide:
carbon
oxygen
carbon
dioxide
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
But, if the supply of oxygen is insufficient, then carbon monoxide, CO, may be
formed:
C
+
carbon
q
=
oxygen
2CO
carbon
monoxide
Carbon monoxide itself burns in oxygen (or air), forming carbon dioxide:
2CO
carbon
monoxide
+
q
oxygen
=
2co2
carbon
dioxide
As carbon monoxide is a poisonous gas, the incomplete combustion of carbon
can be very dangerous.
To summarize, combustion is the process of burning a substance in air or
oxygen so that it forms new chemical compounds with oxygen. It is therefore a
chemical change. Oxygen is essential for combustion. In most circumstances
ordinary air provides an adequate supply of oxygen for complete combustion.
During combustion heat and often light energy are released.
4 A VARIETY OF FUELS
You have already learnt that fuels provide us with a concentrated source of
energy-but what do we understand by that? Unit 9 of S102 introduced the
concept that energy is a means of doing work or producing heat and is measured
in joules. You will also recall that energy can be, and is, converted from one
form to another; but conversion of energy always involves losses to forms-of
energy other than the form of energy required. For example, in a light bulb the
energy is not only converted to light-the desired form; some energy is
converted to heat. We buy energy, in the form of electricity, gas or petrol, but in
fact we do not use it-we make it do work for us, and in so doing the energy is
converted.
COAL
Coal has been used as a fuel by humans for hundreds of years. It is mined from
varying depths below the Earth's surface in deep-shaft, open-cast or drift mines.
Today this is an intensively mechanized process.
Coal is formed from the remains of plants and trees that grew in tropical forests
some 300 million years ago (during the Carboniferous Period, see Section 3 of
Units 28-29 of S102). When trees and other vegetation died they were gradually
covered by many layers of water-borne sediment. As the layers of plant material
became more deeply buried they were compressed and heated. Over hundreds of
millions of years this resulted in the transformation of rotting vegetation into
coal.
Coal therefore consists of a mixture of chemical compounds containing
principally carbon, sulphur, nitrogen, oxygen and hydrogen.
At the time when the vegetation grew, it was sufficiently plentiful that during
the process of photosynthesis (you will learn more about this in Section 8 of
Unit 22 of S102) the plants and trees absorbed large amounts of carbon dioxide
from the atmosphere and released oxygen. Today large amounts of coal are being
burnt, which is releasing vast quantities of carbon dioxide into the atmosphere. It
appears that the vegetation covering the Earth today is not sufficient to absorb
all this carbon dioxide, so the amount in the atmosphere is gradually increasing.
Any increase in the concentration of carbon dioxide in the atmosphere leads to an
increase in the 'greenhouse effect' and thus to an overall rise in global
temperatures. This is one of the reasons for worldwide concern about the
indiscriminate destruction of tropical rainforests, which further reduces the
SCIENCE FOR PRIMARY TEACHERS
world's vegetation and leads to a decrease in the amount of carbon dioxide that is
absorbed.
Coal that is being used now was formed around 300 million years ago, and is
therefore a non-renewable source of energy.
PEAT
Peat is an early intermediate stage in the formation of coal. It is found on or very
near to the Earth's surface and has not undergone compression in the same
manner as coal. When peat is dug out and dried it can be burnt. It is commonly
used as a fuel in Ireland.
LIGNITE
Lignite is so-called 'brown coal'; it is 'young' coal that has not undergone all
the stages of compression, though it is very much closer in age to coal than it is
to peat. Lignite has a crumbly texture and often shows signs of the plant
material from which it was formed.
Coke is made from coal by heating it in an airtight oven. Since air is excluded
the coal cannot bum. The heat removes oily and tarry substances together with
ammonia and other gases from the coal. The residue is coke, which is hard and
full of tiny holes. Numerous products can be made from the oil, tar and
ammonia and other gases that are separated out. Coke is almost entirely carbon
and it releases more heat energy than does the same quantity of coal. Hence coke
is chosen for use where particularly high temperatures are required, for example
in steel production.
CHARCOAL
If burning wood is covered to keep air from getting to the fire, it will still burn
slowly because a certain amount of oxygen is present in wood itself. When wood
burns in this way it gives off various gases, and what remains is the black
substance we know as charcoal. Charcoal makes a good fuel because it is almost
all carbon and, as with coke, its combustion releases much more heat energy
than would be released by the combustion of the same amount of wood.
OIL, PETROL AND.RELATED PRODUCTS
Oil, as extracted in its crude unrefined form, from deposits such as those under
the North Sea, is a mixture of similar chemical iompounds ranging from
substances with low boiling points, such as petrol or kerosene, to tarry sludge.
(In S102 some examples are given in Table 4 of Section 3.1, in Units 17-18.)
Oil is formed as a result of the-decomposition of dead organisms. Crude oil from
different locations and depths around the world varies in composition and
contains different amounts of each compound.
REFINING OIL
One component of crude oil is gasoline or petrol as used in car engines. In the
refining process the crude oil is heated to about 350'C. Non-volatile
components of the mixture do not vaporize under these conditions; they remain
liquid and are collected to use in, for example, road surfacing. Some can be
broken down (by a process known as 'cracking') into mixtures of smaller
molecules, which can then be further refined. Components that boil at lower
temperatures are separated from each other and from the tarry residues by the
distillation process. These 'fractions' of the mixture range in boiling temperature
from bottled gas, used for domestic fuel, through gasoline or petrol for cars,
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
kerosene for aircraft fuel, diesel and heating fuel oils, lubricating oils and wax, to
the type of fuel oil used in ships' engines.
The front cover of Units 17-18 of S102 shows the result of an analysis of some
crude oil using the technique of gas chromatography. The principle of gas
chromatography is that if a mixture of substances is passed through a long, fine
tube, which is kept at a certain temperature and packed with a special nonvolatile material, each substance in the mixture takes a different time to emerge,
thus affording a means of separating the components of the mixture.
The cover of Units 17-18 shows that the particular sample of crude od analysed
contained seven principal components. Each was an alkane, a compound of
carbon and hydrogen containing only single bonds. Starting from the right-hand
side, the first two components of the crude oil mixture are C5HI2and C&,,.
Table 2 gives the molecular formulae for different components. Try to complete
the table to show the structural formula and abbreviated structural formula for
each component.
TABLE 2 Formulae of some hydrocarbons
I Molecular formula
Structural formula
Abbreviated structural formula
SCIENCE FOR PRIMARY TEACHERS
PETROL OR GASOLINE
If you were to fill up your car's petrol tank with crude oil, the results would not
allow you to travel very far! Some of the mixture might evaporate too readily
and escape into the air while you were still at the filling station or might be too
volatile to burn in an internal combustion petrol engine. Other components
might be nearly solid, or tarry oil unable to travel through the carburetter.
The internal combustion engine relies on the burning of petrol in air, ignited by
a spark generated by electrical power from the car's battery. The carburetter
mixes petrol and air in specific proportions and this mixture is then directed into
the engine's cylinders, where ignition takes place. When the petrol burns in the
air in the cylinder, exhaust gases are produced; these are the products of the
chemical reaction of the combustion of petrol in the air. They are bulkier than
the petrol-air mixture and push on the piston at one end of the cylinder. The
movement of the piston is transmitted, via the camshaft and gearbox, to the car's
wheels in order to make the car move.
Petrol must b u n in a car engine as efficiently as possible. A fuel that, though it
might bum readily and steadily when first ignited by the engine's spark plugs,
burns suddenly and explosively when there is only a small proportion of it
remaining, is unsuitable. Such sudden combustion causes a rapid expansion of
the gases inside the cylinder and hence an abrupt movement of the piston. This
is what is termed 'knocking' in an engine. It causes uneven running and extra
wear on the engine. It is therefore desirable that a fuel does not bum in this way.
Knocking in a particular engine can be minimized by careful choice of fuel and
by adding a substance to the fuel that will inhibit knocking. Such additives are
called 'anti-knock agents' or simply 'anti-knock' for short. The chemical
composition of the fuel itself can be altered by mixing together different
hydrocarbons in varying proportions and by altering the structure of the
hydrocarbons present so as to produce different structural isomers of one or more
of the hydrocarbons.
Experience has shown that one particular hydrocarbon, iso-octane (2,2,4trimethylpentane), has especially good resistance to knocking. For the purpose
of constructing a scale of anti-knock behaviour, which is known as the octane
scale, iso-octane has been assigned an octane value of 100. Iso-octane is one
structural isomer of the alkane octane CsHI8.
octane
iso-octane (2,2,4-trimethylpentane)
The other end of the scale is represented by heptane, C7HI6,which has the
structure:
CH3-CH2-CH2-CH2-CH2-CH2-CH3
It has very poor resistance to knocking and has been assigned an octane rating of
0. Octane ratings for other petrol fuels are assigned by comparison with these
two compounds. For example, four-star petrol has an octane rating of 99. Car
engines are designed to work best with fuel of a particular octane rating and it is
therefore important to use the recommended grade of petrol.
LEAD IN PETROL
About 60 years ago it was discovered that adding small quantities of certain
compounds of lead would raise the octane rating of a fuel substantially. About
0.5 g 1-I of the compound lead tetra-ethyl (which has the chemical formula
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
Pb(C2H5),) raises the octane rating by about six points. Using a higher
concentration raises the octane rating still further. The higher the octane rating of
the petrol used in an engine, the more efficient is the use of that fuel and the less
the amount of the fuel needed.
lead tetra-ethyl
However, widespread use of compounds such as lead tetra-ethyl in petrol results
in lead being present in the atmosphere in unacceptably high concentrations,
especially near busy main roads or motorway interchanges such as Spaghetti
Junction near Birmingham.
Thus, a balance has to be struck between levels of lead in fuels and the
desirability of reducing the amount of fuel consumed.
VEHICLE EXHAUSTS
0 What are the products formed when octane undergoes combustion?
Carbon dioxide and water, unless the air supply is restricted, in which case
some carbon monoxide may be formed.
octane
oxygen
carbon
dioxide
water
All four substances are present in gaseous form at the time of combustion.
The major components of vehicle exhaust gases are carbon monoxide, carbon
dioxide and water vapour. The water vapour causes few problems. On a cold day
it can be seen as a mist of liquid droplets after it has undergone the phase change
from the vapour. The carbon dioxide, however, adds to that already in the
atmosphere, increasing the dangers from acid rain and the greenhouse effect.
Carbon monoxide is extremely poisonous, combining with haemoglobin in red
blood cells; affected cells are unable to carry oxygen around the body for up to 3
months.
When combustion occurs in an engine, very high temperatures are produced.
Nitrogen, the major constituent of air, is also present at the moment of
combustion, and when subjected to high temperatures it reacts with oxygen to
form oxides of nitrogen. In addition, the fuel itself is likely to contain a small
quantity of nitrogen, which will also combine with oxygen. Oxides of nitrogen
react with water vapour to form nitric acid, another cause of acid rain, and also
take part in the destruction of the ozone layer high in the atmosphere. Some
unburnt hydrocarbon compounds are also released into the atmosphere as exhaust
fumes. Low in the atmosphere, near to ground level, and in the presence of
sunlight, they undergo a photochemical reaction with oxides of nitrogen, one of
the products of which is ozone. Unfortunately, this ozone does little to
counteract the depletion of ozone high in the atmosphere; its main effect is
irritation of the lungs. The term 'photochemical smog' has been coined for air
pollution resulting from exhaust fumes. In London alone, more than 1.3 million
tonnes of pollutants are pumped into the atmosphere each year. It is estimated
that more than 80% of this comes from cars.
As we are now all aware, a major problem with petrol engines is that they cause
atmospheric pollution. To summarize, this pollution is caused by the following:
lead compounds from anti-knock additives such as lead tetra-ethyl, Pb(C2H5),
carbon dioxide, CO2, the main product of the combustion reaction
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carbon monoxide, CO, from incomplete combustion
nitrogen oxides, NO, NO2, formed from air at the high temperatures of the
explosion
hydrocarbons-unburnt or incompletely burnt fuel: 65% in exhaust, 15%
from evaporation, 20% from gases that escape past the piston rings into the
oil sump.
UNLEADED PETROL AND CATALYTIGCONVERTERS
Unleaded petrol now offers an alternative to leaded fuels. It is becoming popular,
largely owing to its 'lower price (once the cost of engine adaptation has been
met) and rising general concern about the effect of all forms of pollution on
people and the environment. However, exhaust gases from unleaded petrol still
contain carbon monoxide, hydrocarbons and oxides of nitrogen, which all
contribute to the production of smog and acid rain.
Catalytic converters, or 'cats', which are sometimes fitted to cars that run on
unleaded petrol, are designed to remove these pollutants from the exhaust fumes.
The 'cat' is placed at the front end of the exhaust system. A full 'three-way'
catalytic converter, now used by many car manufacturers, can remove up to 90%
of exhaust pollutants.
Today 'cats' are spreading through the new car market. The proportion of petrolengined cars equipped with catalytic converters in the new car registrations for
the first quarter of 1991 was 15.6 per cent, compared with just over 3 per cent in
the same period of 1990. After the end of 1992 all new cars will have them, to
comply with new EC regulations on exhaust emissions.
The first significant research into the use of catalytic converters was carried out
in the 1950s by General Motors in the United States. The company based its
work on the studies of Eugene Houdry, who had discovered that the catalytic
method employed to break down crude oil into its constituent parts (petrol,
paraffin, diesel and heavy engine oil) could also be used to remove dangerous
elements from petrol engine exhaust gases.
A catalytic converter works by catalysing basic chemical reactions. When the
car's exhaust gases reach the converter, they pass through a honeycomb-like
structure, called a cellular ceramic substrate. This is coated with a thin layer of
platinum and other precious metals, which act as catalysts, beginning reactions
that change the chemical composition of the gases.
Platinum and palladium promote the conversion of unburned hydrocarbons and
carbon monoxide into carbon dioxide and water vapour. Rhodium catalyses the
conversion of oxides of nitrogen and hydrocarbons into nitrogen and water,
which are harmless. Although 'cats' are only about 30cm long by 23cm wide,
the substrate's total surface area is 23 000 m2, the size of two football pitches.
While the widespread use of unleaded fuels and catalytic converters would cut
pollution levels drastically, there are still some drawbacks. Under certain'
conditions, catalytic converters make possible a chemical reaction between
sulphur (which is present in petrol in small quantities) and hydrogen. The
product of that chemical reaction is hydrogen sulphide, a gas that smells of
rotten eggs. You sometimes get a whiff of it when cutting open a freshly
prepared hard-boiled egg.
hydrogen
sulphur
hydrogen
sulphide
Hydrogen sulphide is highly toxic and a concentration of 1 part in 1 000 can be
lethal in half an hour, but cars fitted with catalytic converters produce much
smaller quantities than this. It is thought that the amount of hydrogen sulphide
produced as a result of the use of catalytic converters will merely cause minor
annoyance from the smell rather than presenting a serious health hazard, and that
.-
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the environmental gain from using unleaded fuel and catalytic converters will far
outweigh the nuisance of the occasional unpleasant smell.
Another side-effect of the use of unleaded fuels is the increased proportion in
exhaust fumes of benzene, which is toxic, carcinogenic and volatile. When a fuel
that contains benzene is used, small amounts of it are released into the
atmosphere. All petrol contains small quantities of benzene, but lead-free petrol
contains a slightly larger proportion than traditional leaded fuels. Hence the use
of unleaded fuels will cause a small rise in the amount of benzene present in the
atmosphere.
Finally, using unleaded petrol and catalytic converters does nothing to reduce the
amount of carbon dioxide that is pumped into the atmosphere by cars.
THE OZONE LAYER
Ozone in the upper atmosphere (the stratosphere) prevents radiation with
wavelengths below 290nm from reaching the ground. Radiation of around
265 nm is most dangerous to living things, including the plants on which we
are ultimately dependent. Ozone also stops a great deal of radiation in the 290320 nm range, implicated in the development of skin cancer.
Concentrations of ozone in the stratosphere fluctuate with natural changes in the
rate of its production and destruction. The rate of production of ozone appears to
be out of our control, but the compounds we add to the atmosphere increase the
rate of its destruction. Worldwide concern about this has resulted in an
international agreement to limit the release into the atmosphere of certain
compounds, notably chlorofluorocarbons, or CFCs. The reactions of the
atmospheric gases in the environment and the unpredicted effects of quite small
disturbances provide us with a superb example of the delicate balance of
chemicals in the environment.
The process is as follows:
Ultraviolet (u.v.) light splits an oxygen molecule, 0 2 , into two atoms of
oxygen, 0:
U.V.
q +o
+ o
The oxygen atoms can react with other oxygen molecules to produce ozone, 03:
0+0
2
o3
Or they may react with ozone to produce oxygen molecules again:
When ozone absorbs
oxygen atom again:
U.V.
light it breaks up into an oxygen molecule and an
U.V.
Q
+02+0
A delicate balance is set up that regulates the concentration of ozone. (The
concentration is at about 10 parts per million, usually abbreviated as ppm.),If all
the ozone in the atmosphere were at at the Earth's surface it would form a layer
only about 3 mm thick.
In reality, the processes that balance the 'natural' ozone budget (i.e. even in the
unpolluted stratosphere) are more complex than this. Other gases, naturally
present in trace amounts, make the loss of ozone a little faster than it would
otherwise be. Among the first of these gases to be recognized was nitric oxide,
NO. It reacts with ozone to form nitrogen dioxide and an oxygen molecule:
NO
+ 0, + NO, + 0,
SCIENCE FOR PRIMARY TEACHERS
The nitrogen dioxide then reacts with a single oxygen atom to form nitric oxide
and an oxygen molecule:
This releases another nitric oxide molecule, which can then destroy another
ozone molecule, and so on, in a chain reaction.
In addition to being a filter for ultraviolet light, ozone is an important stabilizer
of our climate. The lowest layer of the atmosphere, the troposphere, is warmed
by the heat reradiated at the Earth's surface. The rising of this heated air, its
cooling high up and then its falling is a major factor in the behaviour of weather
systems. The next layer up, the stratosphere, is heated from space. The ozone
layer absorbs ultraviolet and emits infrared radiation as heat. There is no
convection and little mixing, as occurs in the troposphere below. With less
ozone and hence less absorption, the ultraviolet radiation penetrates deeper and
gives a warmer troposphere and a colder stratosphere, with consequences for our
weather. In addition, increased levels of atmospheric carbon dioxide and methane
(which is increasing three times as fast as carbon dioxide) increase the
greenhouse effect in the troposphere.
CHLOROFLUOROCARBONS AND CHLOROCARBONS
Although not directly related to the topic of fuels, a discussion of CFCs and
chlorocarbons (members of the halocarbon family) is relevant here as they are
very important with respect to the destruction of the ozone layer. At one time
refrigerators used ammonia gas and aerosols used butane. However, ammonia is
poisonous and has a very unpleasant smell, and butane is very flammable. Two
chlorofluorocarbons, CFC-11 (CC13F) and CFC-12 (CC12F2),were introduced in
the 1930s as refrigerants, and after the Second World War as aerosol propellants.
In 1975 something like 3 000 million aerosol cans ejected more than 500000
tonnes of fluorocarbons into the atmosphere. These compounds are nonflammable, odourless, non-toxic, except at very high concentrations, and
chemically very stable, so that they do not react with the can contents-what
more could we ask for? Because of their different boiling points and vapour
pressures, the two CFCs were useful for different applications: CFC-12 gives
the type of high-pressure spray needed for insecticides and paints, while CFC-11
gives the more gentle spray needed for hairspray, perfumes and deodorants. In
1951 another use was found for these fluorocarbons: as a non-flammable
foaming agent to replace pentane in the production of the foam plastics
polyurethane and polystyrene.
The major uses of another chlorofluorocarbon, CFC-13 (CC12FCC1F2),are in
the electronics industry, for dry-cleaning and in aircraft maintenance. It is one of
the few solvents that is non-toxic and does not attack electronic components.
Unfortunately, the stability of CFCs, which was considered one of their main
advantages, has resulted in a rapid build-up of their concentration in the
atmosphere. It is this build-up that has led to some of our current atmospheric
problems. A study published by the CSIRO Division of Atmospheric Research
gives the annual percentage increases in concentrations of CFCs and
chlorocarbons in the atmosphere. Some of their results are shown in Table 3
together with the half-lives of some of the materials in the atmosphere. (The
half-life of a material is the time taken for a quantity of that material to be
reduced by half.)
TABLE 3 Annual increases in some CFCs and chlorocarbons in the atmosphere
Substance
Formula
Annual increase/%
CFC- 1 1
CFC-12
CFC- 13
trichloroethane
carbon tetrachloride
CC13F
CC12F2
CCl2FCC1F2
CH3CC13
CC14
5
5
13
5
1-2
Half-lifelyears
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
The chlorofluorocarbons in aerosols have now been replaced to some extent by
trichloroethane, CH3CC13,which is also used in vapour degreasing. However, as
seen in Table 3, it is also persistent in the atmosphere, although for a much
shorter time.
Reactions
In the upper atmosphere, the unfiltered U.V. irradiation breaks up the halocarbons
to produce chlorine atoms with varying efficiency. In a reaction similar to that
described for nitric oxide and ozone, a chlorine atom, Cl, from a
chlorofluorocarbon can combine with ozone, 0 3 , to form C10 and an oxygen
molecule, 0,. Then C10 and an oxygen atom, 0 , combine to produce another 0,
and a free chlorine atom, Cl, again.
The initial ozone is lost, and since the chlorine atom is regenerated, it can go on
and repeat the process in a chain reaction. Because of this regeneration, every free
atom of chlorine in the stratosphere can destroy as many as 100000 molecules
of ozone. It will eventually be removed from the chain by reacting with some
other atmospheric impurity such as methane, forming hydrogen chloride, which
in turn contributes to acid rain.
The relative effect that CFCs have on the ozone layer is thus a function of how
efficiently they are broken down by U.V.irradiation as well as of their
persistence.
Ideas for teaching relating to environmental problems such as the ozone layer are
included in 'The chemistry of carbon compounds' and the Study Commentary for
Units 28-29.
5 CONCLUSION
We started by looking back at earlier work done on energy and its necessity to
life. In looking at fuels we have been specifically concerned with aspects of
fossil fuels-how we u s e thein and the problems they generate for the
,
'
environment.
At this.point, it may be appropriate for you to consider how some of these
concepts can be introduced to young children. Because of the extensive media
coverage, many of us are aware of issues such as diminishing oil resources and
environmental~problemsassociated with the use of fossil fuels. Although this
topic is limited in its approach it should be clear that many issues are involved;
consequently there is no single easy way to handle the topic. Our intention here
is to provide some knowledge about the'science related to fuels to enable you to
address such issues scientifically and plan your teaching more effectively.
SCIENCE FOR PRIMARY TEACHERS
MATERIALS
1 INTRODUCTION
This part of the chemistry materials focuses on children's ideas about what
materials are and why they are different. We look at how the chemistry that you
have already met helps you to plan tasks that will support and encourage
children's learning.
..
-.7
'The materials that we use every day' is a common topic in primary schools. In
Section 4 we consider how the chemistry relating to materials can help us to
better understand these common items. The progress made by chemists and other
scientists in the understanding of materials has given us our current technology.
The whole fabric of our society, literally and metaphorically, depends on our use
and development of materials.
In recent years the rate of change of material development has been rapid; terms
such as computer, plastic, nuclear and silicon have quickly become part of our
everyday vocabulary. One reason for this rapid rate of change is that we now
have a better understanding of the chemistry that governs the technology.
Theories and principles attempt to rationalize and explain the vast body of
experimental evidence that we now have about the behaviour and properties of
atoms, molecules and hence materials themselves. With these theories and
principles to support them, chemists can modify materials in order to change
their characteristics. Improvements can be made to a material's strength,
conductivity, durability or any one of a number of other properties.
Using this topic as a source of ideas, you can use your own science knowledge
to plan your work effectively and to help children make more sense of the world
around them.
2 MATERIALS-WHAT
ARE THERE?
KINDS
Every day we use many different materials: metals, plastics, paper, wood, glass,
brick, textiles and water, to name but a few. Each has its own particular
characteristics, which determine its use. For example, some materials conduct
heat, some conduct electricity, some corrode, some are stronger or stiffer or
tougher than others, and so on.
So the term materials is used to cover a wide variety of objects with vastly
differing physical characteristics. But what does the term mean to you?
ACTIVITY 1 :
WHAT IS A MATERIAL?
Spend some time thinking about what is meant by the term material. Draw
up a list of all the different materials you can think of. You might want to
start this exercise by just looking around you; what types of materials do you
see? What about materials with specific uses other than in a house or office?
Keep your list, as we will come back to it later.
The b n c i s e Oxford Dictionary defines material as 'the matter from which a
thing is made'. This is a very broad definition. It means that everything around
us-solid, liquid or gas-is a material. Did your list contain gaseous and liquid
materials as well as solids? It is perhaps more common to think of materials in a
structural sense as solid materials, and this is the usage that we will employ
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
here. In doing so we arbitrarily rule out of our discussion liquids and gases,
although the same general principles that will be developed for solids will also
apply to these states.
In the classroom a good way to focus children's thinking about materials is to
set up a display with a series of questions nearby that prompt the children to
think about what they see.
I ACTIVITY 2:
MATERIALS DISPLAY
Discuss with your colleagues at a tutorial session the different materials that
you would include in such a classroom display and devise some prompting
questions. Compare your answer with the suggestions below.
-Your display should include a collection of everyday materials that serve to
arouse interest and ensure engagement with the topic. For example, foodstuffs
and other items from the kitchen, plastic and metal objects, cloth, building
materials and household items such as paint, oil and polish. Both natural and
manufactured items should be represented, as should the three states of matter.
The questions positioned near to the display might include:
What do you know about each material?
What do you notice about each material?
What could you do to any of the materials to find out more about them?
Encourage the children to think about and record their answers to these questions.
(CAUTION-If this type of activity is done in the classroom you must be aware
of the safety implications of such a display; warn children about the dangers of
smelling, tasting and touching unknown substances.)
3 USING MATERIALS TO
DEVELOP PROCESS SKILLS
Activities that focus on materials provide numerous opportunities to develop,
record and assess the skills required for AT1. Because of this, we take some time
here to look at the process of observing and ask you to carry out some Activities
with your colleagues. We begin with a group of tasks that emphasize the
complex nature of observing and then go on to link observing with the act of
answering questions. The next step is to demonstrate how you can systematize
the process by controlling variables. We end this Section with an example of a
fair test and a discussion to relate the work to the national curriculum. Wherever
possible, you should try to do these Activities at a tutorial session or with
colleagues at school, working in small groups of four or five.
USING OBSERVATION IN INVESTIGATIONS
OBSERVING AND RECORDING
It is no exaggeration to say that without observation there would be no science.
Observation is the very foundation of the sciences, and learning to observe in a
systematic and disciplined way is the essential first step toward becoming a
scientist or learning to appreciate science. Observation is an active process, and
to understand it you must do it. Things that at first appear to be the same or very
similar can be remarkably different Distinguishing between them may require a
number of different observations. Sometimes the differences are clear to just one
of the senses; things may look the same but feel different, for example. Or
perhaps the differences only become clear if observed on a different scale-by
SCIENCE FOR PRIMARY TEACHERS
using a hand lens, for example. In other cases the difference is not in how
materials appear but in what they do or how they behave in certain
circumstances.
ACTIVITY 3: MAKING, RECORDING AND
DISCUSSING OBSERVATIONS
You will need:
a collection of white solids (granulated sugar, salt, icing sugar, flour, plaster
of Paris, crushed ice, liver salts, etc.)
hand lens
balance
spoon
containers (cups, yoghurt pots, etc.)
water
Set out the selection of white solids, and examine them thoroughly. Now add
a small sample of each in turn to some water and stir. Record your
observations.
Discuss with your colleagues the observations you made and how you made
them. Try to answer the following questions:
When examining the solids, did you use all your senses?
Did you consider the safety of handling unknown substances?
When did you decide how to record your observations?
Did you make measurements of any sort?
When recording your observations, did you use any 'scientific' words,
such as 'dissolve' or 'melt'? What is the difference between, for example,
'the splid disappeared' and 'the solid dissolved'?
ACTIVITY 4: ANALYSING OBSERVATIONS
Observing is not as simple as it may seem, and often includes more than one
process.
Go back to your recorded observations and, using the colour coding given
below, underline the parts of each record that fall into the categories (a) to (e):
I
1
1
1
I
.
.
(a) describing things or happenings (black)
@) classifying things or happenings (blue)
(c) comparing things or happenings (green)
(d) measuring things (yellow)
(e) interpreting things or happenings (red).
Have you underlined any of your observations in more than one colour? This
Activity vividly illustrates the complexity of even these apparently simple
observations.
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
RAISING QUESTIONS
Although observing is clearly a complex process, it is not complexity itself that
makes an observation scientijic. It becomes scientific when it is guided by a
scientific purpose-that is, when it is used to answer certain sorts of questions.
Using scientific observation to answer questions is very useful in many subject
areas; good teaching fosters the ability to transfer skills from one area of activity
to another and to apply skills.
ACTIVITY 5: RAISING QUESTIONS FOR
INVESTIGATION
You will need:
hand lens
three boxes labelled A, B and C containing:
box A-various
samples of rock
box B-various
samples of coloured crystals
box C-various
flower heads
box A-various
face cloths and towels
box B-various
different sponges
box C-various
examples of brushes and scouring pads
Open box A. Examine the contents and discuss what questions could be asked
about them. Write down as many questions as occur to you as a result of
your observations.
Open box B. Could all the questions you asked about the contents of box A
also be asked about box B? Write down any new questions that occur to you
after examining the contents of box B.
Open box C. Repeat the exercise to see whether the questions you have
written down so far for boxes A and B also apply to the contents of this box.
Again write down any new questions that you think of.
Discuss your questions to find out:
which of them a child could answer by scientific investigation, assuming
appropriate materials were available
"
which of the unanswerable ones could be restated in a different way so
that, at least in part, the content of the question could be probed by
scientific investigation
what pbservations you would have to make to answer the questions.
CONTROLLING VARIABLES
In Activity 5 you were asked which questions could be probed by scientijic
investigation, and to discuss this you had to think about what makes an
investigation'scientific. An important part of whether or not an activity is
scientific is what the investigator is doing. In the following Activity, there is no
elaborate scientific apparatus; this should enable you to concentrate on what you
are doing in the process of carrying out an investigation. You will be asked to
make some things change while others stay the same, and to observe the
consequences of making the changes.
SCIENCE FOR PRIMARY TEACHERS
ACTIVITY 6: ISOLATING AND CONTROLLING
VARIABLES
You will need:
a sheet of A4 paper
scissors
timer
Take a piece of A4 paper. Hold it up high by the longer sides so that the
faces are horizontal. Let go quickly but gently. Observe what happens and
write down a description of the motion.
Cut the paper in half with the cut parallel to the shorter sides.
Take one of the half-sheets, hold it up high as before, with the faces
horizontal, and let go. Once again, write down a description of the motion.
Halve the sheet again by cutting parallel to the shorter sides and repeat the
experiment. Halve the paper in the same way twice more, repeating the
experiment each time and recording your observations.
Now take the other half of the A4 sheet and cut it in half, but this time along
a line parallel to the longer side. Hold the paper up high by the two shorter
sides, with the faces horizontal, and let go, observing and recording a
description of the motion as before. Repeat the experiment, halving the paper
each time along the longer dimension, recording your observations as you
go.
Now repeat the experiment for the two sets of paper, but this time hold the
paper by two adjacent corners, so that its faces are vertical before letting go.
Discuss the possible variables involved in the experiment, and how the
different activities controlled them.
In each of the activities, which variables remained the same and which
changed?
How did the different ways in which the variables were controlled in each
activity tell you which questions the activities were addressing?
Identify some of those questions.
A FAIR TEST
In scientific investigations some things change (or are variable) while some
things stay the same (are invariable). If a number of things vary at the same
time, it is difficult to see what is happening. If you stop one from changing,
say, or change one in a regular way while keeping the others the same, it
becomes possible to make sense out of observations and to use them to answer a
question. If an investigator sets the values of a variable, for example by
repeating an action every 10 seconds, by adding mass in set amounts or by
changing the surface being investigated, the variable is called an independent
variable, because its values are set by the investigator and can be changed at will.
In the first example the independent variable is time, in the second it is mass and
in the third it is the type of surface.
On the other hand, a variable that the investigator observes but does not control
is called a dependent variable, because its values depend on how it responds to
the controlled changes in the independent variable. So, if a rubber band is
stretched by adding masses in increments of 10 g to answer the question 'How
does the length of a rubber band vary with stretching force?', mass is the
independent variable and length (of the rubber band) is the dependent variable.
Often it is a matter of choice for the investigator which variable is independent
LEARNING AND TEACHING CHEMISTRY THRO'UGHTOPIC WORK
and which is dependent. (How would you investigate the stretching of a rubber
band by using length as the independent variable and mass as the dependent
variable? You may like to refer back to the Study Commentary for Unit 3.)
In Activity 7 you need to identify the v ~ a b l e and
s decide which ones must be
controlled for~thetest to be fair.
ACTIVITY 7: DESIGNING A FAIR TEST
Choose one of the following investigations:
1 Which material will make the best raincoat?
2
Which detergent is best for removing stains?
3
Which paper is best for writing on?
4
Which floor covering is best for a kitchen?
You will need:
1 A selection of fabrics (including, if possible, hessian, canvas, PVC,
gaberdine, nylon, linen, polyester), tin cans, measuring cylinders, beakers and
jugs, rubber bands, string, scissors, timers, a ruler and a hand lens.
2 A selection of various soap powders, liquid detergents, etc., water, a
kettle, fabrics containing assorted stains (tomato, grass, coffee, fat, etc.),
measuring cylinders, jugs, bowl, beakers, pieces of cloth and a timer.
3 Samples of various types of paper (newsprint, sugar paper, blotting
paper, glossy paper, etc.) and a selection of writing equipment (ballpoint
pens, felt-tip pens, fountain pens, pencils, etc.).
4 samples of various floor coverings (carpet of different kinds, lino,
wood, cork tiles, etc.), cleaning materials and sandpaper.
Plan how you will control variables to make the investigation a fair test of
the materials. Then carry out your investigation, recording your observations.
Which variables did you treat as dependent variables and which one was
independent?
Prepare a poster record to indicate:
what you were testing
what you changed systematically
what you kept the same
what you compared or measured.
PROCESS SKILLS IN THE NATIONAL CURRICULUM
Making observations involves many kinds of activity. In science, observations
are made to answer questions, and there is a skill in raising questions that can be
probed by investigations. Often the observations will serve to answer the
questions only if they are carried out systematically, with some of the variables
being controlled.
SCIENCE 'FOR PRIMARY TEACHERS
,
1 ACTIVITY 8:
IDENTIFYING PROCESS SKILLS
Discuss with the rest of your group the observations you made during the
previous Activities; see if you can identify examples from your practical
work of the process skill indicators listed below.
Look at the national curriculum programmes of study for key stages 1 and 2
together with the statements of attainment for AT1, and note which
statements of attainment reflect aspects of the work covered in this section.
PROCESS SKILL INDICATORS
Observing
Using all appropriate senses (CAUTION-Remember
the safety
implications of using all your senses to investigate materials).
Describing observations.
Selecting relevant observations.
Noting similarities, differences and regularities.
Comparing ('is lighter than', 'shorter than', etc.).
Ordering events, sequencing.
Making observations over a period of time (of whole processes, not just the
beginning and end).
Noting any exceptions or unexpected results.
Describing patterns.
Identifying when and where examples fit into a stated pattern.
Classifying (sorting according to one or more attributes; recognizing criteria
used for sorting; devising your own criteria and sorting in several ways).
Measuring
Making an appropriate selection of a measuring device.
Recognizing when estimation is more appropriate than accurate
measurement.
Using measuring devices with a certain degree of accuracy.
Recognizing the variability and reliability of measurements, and the need to
repeat and check measurements.
Recognizing the arbitrary nature of units.
Raising questions
Raising as many questions as possible.
Identifying those questions that can be answered by scientific investigation
and those that cannot (considering availability of resources and stage of
development of the child).
Reformulating questions into a form that can be tested.
Being able to define a testable question.
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
4 CLASSIFYING MATERIALS:
DESCRIPTION AND PROPERTIES
Our earlier discussion of materials concentrated on solids. However, as you have
seen, solid materials is still a very broad term covering such diverse solids as
paper, sand, steel and fabric. If we are to try to rationalize and explain their
properties in chemical terms we need to subdivide our materials into more
meaningful and manageable classes.
Children will have many of their own ideas about the groups into which items
can be sorted. Fabrics, metals, rocks, soils and plastics all provide an exciting
variety of colours, textures and properties. Sorting waste is topical and provides
a link to other cross-cumculum themes, such as the environment and the need
for recycling materials.
At key stage 1, young children's vocabulary and ability to describe similarities
and differences will vary greatly. However, in this type of sorting exercise you
should look for the children's ability to notice the properties of the materials and
to sort them accordingly. Hence, the statement 'I can see through this' is just as
valid as 'It's transparent'. Children might be expected to place all fabrics in one
group 'because they're soft' and wood, metals or stone in another 'because
they're hard'. At level 3 a child questioned about the properties of metals might
be able to make predictions such as 'it will feel cold', 'it looks shiny', 'it will
be strong', 'it will be hard', and so on, based on their previous experience of
everyday metal objects.
There will obviously be overlap between the abilities and understanding of
children at key stage 1 and those at key stage 2. At key stage 2 the observation
of everyday materials will become more specific and more quantitative. Thus a
child may note that all the fabrics grouped together are fluffy, and then move on
to subdivide them, for example: 'These fabrics are soft and fluffy-the fluff on
this fabric is over 1 cm tall, but this one's got shorter fluff.'
At the higher end of the ab'ility range of key stage 2, some children will be able
to quantify and compare strengths of materials such as slate and blocks of plaster
of Paris. They could be asked to consider the usefulness of the property being
measured, for example in building structures. Further work could be devised
involving making different mixes of cement and testing them for strength.
This type of exploratory work with the children on describing and classifying
materials is of enormous use to you as a teacher since it helps you to address
questions such as: 'Do children perceive similarities in the wide range of
materials that make up individual objects?', 'Are they aware of the nature of the
materials of which the objects are made?' and 'What set terms do they use when
they attempt to classify materials?'
The research team of the SPACE project at the University of Liverpool (see
Russell et al., 1991) undertook a detailed analysis of the responses of children in
a classification task. Children in several schools were individually presented with
a number of different objects and materials and asked to put them into sets
'according to what they are made o f . A list of the objects and materials presented
to the children is given in Table 1 (overleaf). The analysis of the results revealed
more than 50 different set terms that were used to classify the range of objects.
SCIENCE FOR PRIMARY TEACHERS
TABLE 1 Objects and materials that children were required to classify
steel wool
sand
plastic bag
apple
nails
plastic cup
potato
newspaper
white wood
brick
cotton cloth
tomato
aluminium foil
sugar paper
brown wood
milk-bottle top
copper pipe
cutlery
white bread
clay
brown bread
wool
rice
pebbles
candle
lettuce
It was found that criteria other than those having a bearing on what the objects
were made of were used. Criteria used by the children were classified as follows:
Compositional-what the objects were actually made of. Examples
included: metal; plastic; wood; 'material'; soil; stone; polystyrene; plant.
Functional-what the objects could be used for. The sets were of objects
that could be used in the same way: food; building materials; drink; things
that hold things; things to write on; art materials; things with everyday
uses; things we use a lot; things we cannot eat; things used in the kitchen.
Locational-where objects might be found. For example: natural things1
things found in nature; inside things; outside things; things found on the
ground; things seen on the beach.
Perceptual-how .objects were perceived to have observable properties in
common. Sets included: hard; soft; shiny; solidl'unsolid'; crackly; thin;
heavy; squashy; shiny and smooth; changeablelnot changeable; bendy; juicy;
wet; silver; things that feel the same; things that make a noise.
Manufactured-whether
the objects were artificial or natural.
Other categories-a catch-all group for the odd and idiosyncratic Sets that
children produced, often because they could not think where else to put the
objects remaining at the end of their classification. For example: odd ones
out; the 'nothing' group; things that begin with the letter 'p'.
The teachers reported that children were willing to attempt the classification task
as posed, and indeed showed evidence of some deep thinking. However, it became
clear that many children were inclined to classify by reference to criteria other
than those that the task had attempted to define, for example by reference to what
the item was used for rather than what it was made of.
ACTIVITY 9: CLASSIFYING MATERIALS
You have seen how children group objects; now look back at the list you
made in Activity 1. How would you classify the solid materials on your list?
What sort of categories would be most appropriate? Can you group them all
into four or five different categories? Spend some time thinking about this
and note down your classification. You may then wish to compare your
attempts with the classification outlined below.
A CHEMIST'S CLASSIFICATION
..
.. -
-
There are a number of ways in which you could approach this problem. You
might have chosen to divide the materials into groups that reflect the uses to
which they are put (such as building materials, fabrics, conductors, writing
materials, etc.) or their strength (hard, soft, bendable, fragile, etc.).
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
One way of classifying these solid materials is by the chemical nature of the
material itself. A classification along these lines is outlined below; you may
have used some of these categories in your own classification.
Metals. You will, of course, be familiar with copper, iron, aluminium and
other metals from the tremendous variety of their everyday applications-for
example, saucepans, cars, aircraft, filing cabinets, etc. A pure metal is
composed of atoms of a single chemical element. However, metals can be
blended with other elements-usually other metals-to form mixtures
known as alloys, which have altered properties. For example, brass is an
alloy of copper and zinc, steel an alloy of iron with carbon (a non-metal) and
other elements.
Plastics or polymers. The word plastic is used to denote synthetic materials
made from carbon-based chemical compounds that can be moulded to shape.
These compounds consist of very large molecules that are manufactured by
joining smaller molecules (called monomers) together to make long chains.
This process is known as polymerization, hence the term polymer.
' Examples of plastics or polymers include polythene, PVC (polyvinyl
chloride), polystyrene and nylon.
Natural materials. These are animal or plant products, for example wood,
leather and cotton.
Ceramics. As a class, ceramics are made from non-carbon-based chemical
compounds. Examples are the oxides of magnesium, MgO, and silicon,
SiOz (quartz or sand, which is the basis of glass), and alumino-silicates.
Common ceramic products include building bricks, tiles, table china and
concrete.
This is a rather crude classification but it will do as a working model. As with
many classifications, the boundaries between the classes are not always distinct.
We now need to consider the chemistry of this classification and ask whether
there is any chemical rationale for it.
Where does chemistry enter into this classification? If the theories of bonding in
chemical elements and compounds that you met in 'Introducing chemistry
concepts' are to be useful, then we should see some sort of correlation between
the properties of a material and the type of bonding existing between the atoms
and molecules. You might like to look back to Section 6 in 'Introducing
chemistry concepts' before reading on.
Let us take each group in turn and summarize its chemistry from what you
already know.
METALS
Metal is a term that is in common everyday use, but what do you understand by
it? Activity 10 asks you to think about the characteristics you consider to be
typical of metals.
ACTIVITY 10: CHARACTERISTICS OF METALS
What characteristics would you say were typical of metals? Spend a few
minutes listing these and then compare your answer with those given in
Table 2 (overleaf).
TABLE 2 Some general properties of metals
Metals are:
conductors
Meaning
they
conduct
both heat and
electricity
malleable
ductile
lustrous
hard
heavy
sonorous
they can be bent permanently out of
shape
they can be drawn into a wire
they have a shiny appearance
the bonds between their atoms are
strong
they have a high density
they ring when hit with an object
However, there are notable exceptions to these general properties. Gold and
potassium, for example, are soft metals; sodium has a low density and will float
on water; and what about mercury, which is a liquid at room temperature? It is
certainly not sonorous in the liquid state! The only property that they all share is
that they all conduct heat and electricity.
Metals belong to Groups I and I1 of the Periodic Table, and you can predict from
its position in the Table whether an unknown element is a metal or a non-metal.
Metal is thus a broad term used to classify elements that can have very different
properties. Chemists need to understand these properties in order to select the
best metal for a particular application. You can read more about metals in Units
13-14 of S102.
PLASTICS OR .POLYMERS
Plastics are very familiar materials. They have a rather dubious reputation, with
the term often being used in a derogatory way to indicate that something is cheap
and nasty. The poor reputation of plastic materials arose because when they were
first developed they provided much cheaper and often inferior alternatives to
traditional materials for the bulk production of many goods. Nowadays they are
used in a wide variety of applications, from raincoats and golf tees to
replacement hip joints and satellite dishes, and it is hard to imagine the world
without them. Plastic technology has come a long way, thanks to an increasing
understanding of the chemistry involved in the structure and bonding of
materials.
Before we can examine the chemistry of these compounds we first have to
overcome a slight language barrier. You will be quite familiar with the term
plastic; however, chemists tend to call the same materials polymers (from the
Greek polumeros, meaning 'having many parts'). The two terms reflect the
different approaches to the topic and are not an indication of different materials or
characteristics. As we are looking at these compounds from the point of view of
their chemistry, we shall call them polymers.
Now let us consider the chemistry of these compounds. Polymers are made up of
chains of atoms. These chains can be thousands of atoms in length or they can
be relatively short. They are formed by bonding together much smaller
molecules called monomers in a process known as polymerization (see
Figure 1).
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
H
...
+
H
\
/
/
\
C=C
H
H
H
+
H
\
/
/
\
C=C
H
H
+
H
\
H
/
H
\
/c=c +
C=C
\
H
H
H
/
/
H
\
+
...
H
H H H H H H H H
I I , I
I I I I I
FIGURE 1 The polymerization of ethene monomers to give the polymer
polyethene, commonly known as polythene.
Most polymers are based on carbon, which, as you have seen in 'The chemistry
of carbon compounds', has a chemistry all of its own. As you may recall, the
chemistry of carbon is dominated by covalent bonding, either in simple covalent
molecules such as methane, CH,, or extended covalent compounds such as
polymers. In all cases the valency of the carbon atoms is four.
This should immediately lead you to ask why carbon has such a varied and
extensive chemistry that is different from that of most other elements in the
Periodic Table.
Let us try to answer this question by thinking about carbon in the context of
what we know about electronic configuration, the Periodic Table (which is really
a reflection of the variation in the electronic configurations of the elements) and
bonding.
0 What is the electronic configuration of carbon?
H ls22s22pZ.
0 What type of bonding would you expect carbon to show?
H Carbon is a non-metal, although it does have some metallic properties (for
instance, the graphite form is a conductor). It is in the middle of the Periodic
- Table, so to attain the structure of the preceding or next inert gas it would
have to lose or gain four electrons, respectively. The amount of energy that
would be required to do this is so great that it rarely happens. Thus carbon
attains the next inert structure by sharing electrons in covalent bonds.
0 How many covalent bonds will carbon have to form?
H Carbon needs to gain four electrons, so it will have to form four covalent
bonds; in other words, the valency of carbon is four.
But let us return to our polymer chemistry. Polymers can have a wide variety of
different properties--compare clingfilm and a telephone, for instance. How can
this come about if they are all based on carbon with a valency of four?
The polymers are based'on long carbon chains, with other atoms (most often
hydrogen) bonded to the edges of the chains to satisfy the valency (see Figure 2a
overleaf). But we can,link the chains together (see Figure 2b) and still keep the
valency of carbon as four. We can even vary the degree of bonding: Figure 2b
shows a low degree of bonding; Figure 2c shows a high degree of bonding.
SCIENCE FOR PRIMARY TEACHERS
FIGURE 2 Carbon-based polymers showing varying amounts of bonding between
chains.
C3
What different properties would you expect the three polymers shown in
Figure 2 to have?
In Figure 2a there are only weak forces between the individual molecules,
thus it is fairly easy for one chain to slip over the next chain. If there are
chemical bonds between the chains, as in Figure 2b, then these would have
to be broken for this slippage to occur, thus the strength of the material will
be greater. If there are more bonds, as in Figure 2c, the material will be even
stronger.
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
Of course, there comes a time when if you form too many of these bonds
linking the individual chains together you may lose some other necessary
property of the polymer, such as the ability to be moulded into a particular
shape.
Fibres
One of the areas in which the classification of materials outlined earlier breaks
down is in the area of fibres. Fibres are polymers, but they may be natural or
synthetic. The silkworm produces a natural polymer in the form of a continuous
filament which may be up to one kilometre in length. In recent years the
development of synthetic materials such as nylon has resulted in the commercial
production of fibres that have similar, and in many cases (but not all) improved,
properties to those that occur naturally.
NATURAL MATERIALS
Many naturally occurring materials, such as cellulose (wood or plant-stem fibre),
proteins and nucleic acids (for example DNA and RNA), are polymers. The
structures of these molecules are quite complex, but they are all based on
extended covalent bonding between carbon and its near neighbours in the Periodic
Table.
CERAMICS
Ceramics is a term used to refer to many non-carbon-based compounds, quite
often oxides. The name ceramic comes from the Greek keramos, meaning 'burnt
earth', reflecting the fact that they originated from clay-based materials. Ceramic
materials were used to make some of the earliest artefacts, probably because they
could be easily shaped at room temperature before being permanently hardened by
heat.
Ceramics are valuable in all of their many applications because of their ability to
withstand heat and chemical attack.
How do ceramics differ from polymers? In chemical terms ceramics are quite
complex structures, which can vary widely with the nature of the ceramic
material. To simplify matters, let us examine the structure of some of the
naturally occurring ceramics, the silicates. These are the compounds that make
up around 95% of rocks and clays.
There are many types of silicates, but they are all based on different arrangements
of the same chemical unit, a silicon atom surrounded by four oxygen atoms, as
shown in Figure 3.
FIGURE 3 The basic structural unit in silicates.
Silicon is in the same Group as carbon and so will also have a valency of four.
This valency is satisfied by four oxygen atoms, so the basic unit is S i 0 4 .
However, in this structure the valencies of the oxygen atoms have not been
satisfied, so the correct formula for this unit is s ~ o ~ ~with
- , each oxygen atom
carrying a negative charge. Overall the molecule must be neutral. This can be
achieved in two ways. Either the oxygen atom can form a covalent bond to
another atom, or it can form an ionic bond with a suitable positively charged
metal ion.
SCIENCE FOR PRIMARY TEACHERS
Like the carbon-based polymers discussed earlier, the simple
units can
link together by forming Si-0-Si
covalent bonds to form long-chain
polymers, as shown in Figure 4.
I
I
FIGURE 4 Long-chain silicate structure (see Figure 5 for key); the dotted line
indicates the basic repeating unit.
The repeating unit in this polymer is shown between the dashed lines. It is made
up of one silicon atom and three oxygen atoms. Thus the basic structural unit is
still Si04, but the repeating unit is now s ~ o ~ ~since
- , only two of the oxygen
atoms have not satisfied their valencies by forming Si-0-Si
linkages. The
chains themselves can be linked together to form layers or sheets, as in Figure 5.
0 oxygen atom
@ silicon atom at centre of structural unit
obscured behind oxygen atom
FIGURE 5 Layer structure of a silicate; again, the dotted line indicates the basic
repeating unit.
This is a polymeric structure, and again the basic repeating unit is outlined. It is
difficult to recognize this as the basic repeating unit, but the repeated joining
together of this unit will give the total structure.
0 What is the chemical formula for this repeating unit?
The repeating unit will be si2oS2-.
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
An example of this type of silicate is one with a partial formula (Si205)2(OH)2
It consists of two of the polymeric sheet layers, with the hydroxide (OH-) ions
sandwiched between them. However, this cannot be the complete formula since
overall the molecule must be neutral. In this molecule magnesium ions, M ~ ~ + ,
provide the ions to counterbalance the charge. Figure 6 shows the ring
in emerald; here it is usually cr3+ ions that
arrangement of the ~ i 0 2 units
balance the charge on the silicate structure and give emeralds their characteristic
green colour.
FIGURE 6 The ring silicate structure of emerald.
0
How many magnesium ions will there be to balance the charge in a
compound with the formula (Si205)2(OH)2?
We have two
units and two OH- units, so overall there is a net
charge of 6-. Therefore, there will need to be three magnesium ions to
ensure overall electrical neutrality, and the formula is Mg3(Si205)2(0H),.
So we have a balanced formula for this compound.
0
What properties would you expect this compound to have? (Hint:
Can you
think of a compound that has a similar layer structure?)
We have two parallel sheets of atoms that form a type of sandwich. There is
ionic bonding between the two silicate sheets and the magnesium and
hydroxide ions that form the 'meat' in this sandwich, but no bonding
between one sandwich and the next. This is similar to the graphite structure,
which contains just one such plane, so we might expect it to have similar
properties.
Mg3(Si205)2(OH)2is the chemical formula for talc. It does have similar
properties to graphite in that one sandwich can easily pass over the next, since
there is no chemical bonding between them. This gives talc its characteristic
lubricating properties.
SCIENCE FOR PRIMARY TEACHERS
So the bonding in the 'bread' part of this sandwich is covalent, which is similar
to bonding in polymers; however, there is also an element of ionic bonding.
Positively charged metal ions are incorporated into the structures to
counterbalance negatively charged portions of the chain.
Chemical development has now led to ceramics that are extremely hard and
difficult to break. Modern ceramics are used, for example, in turbine blades,
which have to withstand very high temperatures and stress. Ceramics used in this
sort of product are carefully prepared to have highly ordered structures with a
high degree of linkage between the chains.
Now, atoms in metals form ordered structures similar to those of crystalline
ceramics, but we know from experience that metals are electrical conductors and
ceramics are insulators.
0
If ceramics contain metals and also have highly regular structures, why is
one a conductor and the other an insulator?
You will recall from 'Introducing chemistry concepts' that electrons are
negatively charged particles. When these charge-carrying electrons are caused
to move they constitute an electric current. The difference between metals
and ceramics is that in metals the outer electrons are free to move through
the material, whereas in ceramics the outer electrons of the metal are
involved in the formation of ionic bonds with the polymer chain.
Using your knowledge of elements and bonding you should now be able to make
sense of, and justify, a model of classification. In other words, you should now
be able to devise a set of criteria by which to classify materials.
5 DEVELOPING CHILDREN'S
IDEAS ABOUT MATERIALS
Now that we have attempted to make some chemical sense of a classification
relating to materials, let us move on to consider how we might develop
children's ideas about the properties of materials and ways of describing them.
Different activities can be used (a) to encourage children to describe and compare
materials, and (b) to help them to devise ways of investigating specific
properties of materials. We give two examples of investigations here, but there
are many others that you may well have used or could devise.
ACTIVITY 1 1 : MATERIALS IN USE AROUND THE
SCHOOL
Ask the children, in groups, to identify different materials in use in and
around the school. These might be constructional materials (such as bricks,
glass, etc.), plastic for containers, chalk for writing, etc.
Each group could present their findings in the form of a table, or in words
and pictures.
Then let them discuss in their groups (or as a class) why they think each
material was chosen for its particular use. Use questions of the type: 'What
makes chalk a good material for writing with?' If the children are still
working in groups, they might come to an agreement through discussion and
add their agreed reasons to their tables.
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
ORIGINS, MANUFACTURE AND CHANGES
Looking at the origin of a material is a useful way to explore children's
knowledge of the world around them. This work could be introduced by
considering whether or not a material is derived from the living world. A further
distinction between natural and artificial can also be made. Obviously the criteria
for classification will overlap. Also, some items will have more than one
source, for example some fabrics are made from a mixture of natural and artificial
fibres-they are composite materials. However, you do not need to explore these
complexities unless you wish to do so with more enquiring children. Fabrics are
familiar and useful materials for this type of investigation.
At key stage 1 many children will have an idea that some things grow, or are
found in and on the Earth, while other things have to be made in factories.
Although recognizing that cotton in its plant form is natural, children may view
it as artificial when it is made up into a shirt. It is important to eliminate any
confusion by focusing on the material of which the article is made, rather than
the form it takes.
At key stage 2 children might examine rocks containing metal compounds and
compare them with the metals themselves. Salt water could be offered- as a
source of salt, and children could suggest and try different ways of extracting the
salt. (See 'Introducing chemistry concepts' for more information about solutions
and solubility.) The question 'What is useful in air?' might be answered by
looking at products containing gases that are extracted from air: crisp packets are
puffed up with nitrogen; light bulbs contain argon; cylinders of oxygen (liquefied
under pressure) are used by underwater divers and in hospitals. Reference books
will give plenty of information on materials that are based on petrochemicals.
ACTIVITY 12: FINDING OUT WHAT MATERIALS
ARE LIKE
Begin this Activity by getting the children to ask questions about a range of
materials, such as: 'Which piece of metal is the most bendy?', 'Which
materials can you see through?' or 'Is this piece of wood harder than this
one?' You may need to provide guidance as to the most suitable materials to
investigate, but try to let the children plan the actual investigations
themselves. Encourage them to make their tests 'fair'. (You may not be able
to obtain metal strips of identical sizes in testing for bendiness, for example,
but the children could still make a fair comparison by, say, hanging identical
items on each strip to see whether the strip bends.)
Possible properties for investigation are: transparency; mass; volume;
strength; hardness; solubility; flexibility; compressibility.
Work on the origins of materials should always be put in a local context where
possible. Objects from local sources, for example pottery, glass, bricks,
clothing, metal items, paper, plastics and food, can be traced back to their raw
materials. The work provides an ideal opportunity to use both first-hand
experience and secondary sources, such as information from local industry, books
and videos. Always try to use an interactive researching approach when using
secondary sources rather than relying on passive absorption. Discussion with the
children will enable them to appreciate the various processes of change from the
raw material to the finished product. The children could then devise a way of
displaying these changes-for example, using a flow chart such as that shown in
Figure 7 (overleaf).
SCIENCE FOR PRIMARY TEACHERS
clipping
spinning
wool
dyeing
thread
knitting
wool
FIGURE 7 Flow chart showing the origins of a woollen jumper.
If you are able to arrange a visit out of school, the children will gain valuable
first-hand experience. You may choose to visit a local farm to watch the milking
process of a dairy herd, or perhaps a bakery or local industrial museum. Back in
the classroom, the children can record what they have seen using a series of
diagrams.
This type of work may present you with an opportunity to enlist the help of
parents with particular skills or the contributions of children with different
experiences. Whatever finished products you and the children may choose, they
will provide a stimulus to search for details of the processes involved in making
them and so help children to become more aware of where other materials have
come from.
In looking at how materials change you may want to encourage the children to
discover that when chemical changes occur, new substances are formed, but when
physical changes occur no new substances form and the changes are easily
reversed. (See 'Introducing chemistry concepts' for more details.)
Some common examples of changes that happen unless actively prevented can
be explored. For instance, many metals, such as aluminium, zinc, iron and steel,
corrode or rust. These are changes that occur at the surface of the metal,
essentially by reaction with oxygen to form metal oxide. There are many ideas
for investigations here-for example, what will be the effects on the rate of
change of keeping the metal sample warmlcold, wetJdry, greasedlungreased,
paintedhnpainted, and so on. The deposits that form vary according to the metal
and may not be easily visible, but scratching tarnished coins is one way of
showing that the metal has changed at the surface. Polishing achieves the same
result. Dipping coins into acid solutions (for example lemon, vinegar or cola
drinks) 'cleans' the surface and removes any deposit.
Local building stone or rocks can provide a basis for investigating change.
Children could look at how different building stones withstand the elements of
weathering to which they are subject.
Change can also result in a total transformation of a material so that the product
is completely different from the original material. Wellington boots, for
example, are quite different in appearance from the latex they are made of.
Many manufacturing processes will be too complex for children to understand.
However, the concept of 'change' should be relatively easy for them to grasp,
and they may be able to chart the changes brought about by certain processes in
the transition from raw material to finished product, as in the flow chart in
Figure 7. Food processing is an area that can be useful in exploring change-for
example, turning milk into cheese. Some of these processes may involve the
materials in changes of state and so could be used to develop ideas about solids,
liquids and gases.
This type of work provides many opportunities to encourage children to develop
their ideas. A variety of skills can be learnt and used, in particular the ability to
use secondary sources. It may well be difficult to expose the children to many
practical investigations-but this is not to say that the work should not be
tackled. The importance of skills other than practical ones to encourage and
promote learning needs to be appreciated.
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
ACTIVITY 13: FINDING OUT HOW MATERIALS
CAN BE CHANGED
/
Ask the children to investjgate ways in which materials can be changed. As
in Activity 12, materials will have to be selected to match the questions
raised. You will need to consider the safety aspects of this work, as well as
the suitability of a particular material for demonstrating the suggested
changes.
,
Possible changes to look at are those that occur as a result of:
heating or cooking-for
example melting ice, cooking pancakes
mixing or dissolving-for
adding salt to water
example making up a packet pudding mix,
pressing and rolling-for example using Plasticine (use secondary
sources to show the children examples of processes that they cannot
experience directly, such as the pressing and rolling of metals)
bending and twisting-for
shapes.
example using art straws to make different
6 CONCLUSION
The topic of materials is a vast one. Here we have concentrated on the chemistry
and teaching of two concept areas:
descriptions and properties of materials
origins and uses of materials.
Using a variety of different materials you can encourage the children to explore
the reasons for classifi,cation and the criteria used. The large number of possible
criteria makes classification a challenging task for adults as well as children.
Considering the chemistry of materials can help us to sort items into groups,
and offer explanations for differences between materials. It is not difficult to
make a wide range of materials accessible to children in the classroom; the
problem is that some states or forms that are particularly interesting because
they exemplify some key concepts or ideas are extremely inaccessible-for
example, it is not possible to show changes of state for a range of materials.
Thus, we need to be aware that the knowledge of materials assembled from
everyday sources provides a very uneven basis for transition and elaboration from
the general to the scientific domain. If you intend teaching aspects of changes of
state, therefore, you will need to plan accordingly and use appropriate materials.
Initially you may be surprised at the children's lack of knowledge about the
origins of many materials; on reflection, however, it is easy to understand the
reasons behind it. The origins of materials in everyday use are often obscure, and
manufacturing processes are generally hidden from view-they usually take place
in factory environments that do not have open public access. Opportunities to
help children understand these processes may well be limited. The challenge is to
encourage children to think about the materials and to become more aware of the
changes these materials undergo.
Because of the all-embracing nature of this topic, you need to have a clear
framework of what you want the children to achieve. However, the reassuring
message is that a great deal can be achieved through this topic, not only in
science but in many other curriculum areas.
The knowledge of chemistry that you have recently gained should enable you to
enhance the work you do with your children.
SCIENCE FOR PRIMARY TEACHERS
CLEAN SCIENCE
1 INTRODUCTION
This topic explores different aspects of 'clean science'-the science of soaps and
detergents. The work aims to provide stimulating active-learning materials that
can be used as part of an INSET session as well as in the classroom. The
practical work explores how some everyday chemicals are manufactured and
illustrates different aspects of science and technology.
The topic is divided into three parts.
The first (Section 2) involves practical work, in the form of Activities, to
'develop' and 'make' a shower gel, mimicking the approach used in industry. To
cany out these Activities you will need the materials and equipment listed in the
'Introduction to the Study Commentaries'. We advise you not to attempt the
Activities before you have collected together these things. These are practical
Activities and are designed to be done in a group-perhaps
at a tutorial.
However, if this is not possible, you can certainly work through the topic by
yourself. Unlike many of the experiments presented in S102, this work will
involve you in developing and exploring an experimental method. You are
presented with a problem and asked to design the appropriate experimental work
to address it. You are strongly advised to read carefully through Section 2 before
you begin any of the Activities. You will need to plan: (a) how you are going to
work, for example in a large group, combining results, or in pairs; (b) the
possible methods you will use to do the experiment; and (c) what materials and
equipment you will need.
The development of the product represents only one stage in its manufacture.
Product planning, scientific research, market research, economic planning,
advertising and distribution all play a part if the product is to be a success. As
you work through Section 2, think about how these various functions present
many opportunities in the classroom for children to integrate different areas of
the curriculum and for groups of children to take charge of the different areas of
the topic.
Section 3 gives a historical account of soaps, and includes two Activities that
you might like to use in the classroom.
Section 4 provides details of the chemistry of soaps and detergents and suggests
an Activity for class use to find out how detergents work. It also supplies the
relevant chemical information for the shower gel manufacture project.
2 SHOWER GEL MANUFACTURE
These notes are written to help you develop your experimental design skills.
You should also come to appreciate the value of scientific exploration. When
you have completed the Activities, take some time to reflect on how you might
use the ideas in the classroom.
PROJECT BRIEF-THE
PROBLEM
You are in the research and development laboratory of a medium-sized company
that sells personal washing products (soaps, shampoos, etc.). The company's
marketing department has recently received information that one of your main
competitors is test-marketing a new shower gel in a small area of the UK. They
are concerned that your sales of soap will drop when the competitor's product is
launched nationally. They have obtained a sample of the competitor's product
and want you to develop a shower gel that is similar in appearance and properties
so that you can rapidly respond with a 'counter-attack', by selling a new gel
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
product alongside your soap. Your current customers may then stay loyal to your
brand, and buy your gel for the shower as well as your soap for the bathroom.
Your company has a basic formulation for a gel product that was developed in
the past but never used. Many products are partially developed in this way-a
basic formulation is produced but is not marketed at the time. They are often
covered by patents, and hence become useful starting-points for new products in
the future.
Whilst you are developing your new gel product, the marketing department will
conduct trials to determine its perfume and colour. You will need to consult
them before finalizing your product.
(CAUTION-Eye protection and rubber gloves must be worn when handling the
shower gel ingredients and when testing the final product.)
ACTIVITY 1 : ASSESSING THE COMPETITION
You will need:
a collection of five or six commercial shower gel products
Using a variety of shower gels, discuss the properties of the products and
decide which, if any, should be copied.
No doubt you will have included some or all or the following properties that are
important for a gel:
thickness (viscosity)
'latherability' (how easily it foams; what the foam is like; how much it
foams)
pH
'uniformness' (homogeneity).
In the manufacture of your gel we take one of these properties, viscosity, and
examine it in detail. The viscosity of the final product is critical-can you
suggest why? Similar investigations could concern latherability or pH. You
might like to develop these in other sessions.
VISCOSITY-WHAT
IS IT?
Viscosity is usually thought of as a property of a liquid that has something to do
with its 'thickness'. You should remember from 'Introducing chemistry
concepts' that a liquid consists of molecules that can move past their neighbours
but not escape from them completely. Three of the most characteristic properties
of liquids are:
the ability to flow (which is shared by gases)
the possession of a sharply defined surface (which distinguishes them from
gases)
the tendency to vaporize into the space above and to exert a vapour pressure.
All three properties are related to the strengths of intermolecular forces (see
below).
Viscosity is synonymous with 'internal friction' and is a measure of resistance
to flow-the higher the viscosity, the slower the flow.
D What everyday household substances, including foods, can you name where
the liquid's viscosity represents an important property?
SCIENCE FOR PRIMARY TEACHERS
H Cooking oils, treacle, salad cream, sauces, household cleaners, household
bleaches, paint and toothpaste are just a few liquids where viscosity
represents an important property.
0
How do the manufacturers overcome high viscosities so that their products
can be dispensed?
H Products such as mayonnaise and treacle have containers with wide necks so
that the product can be scooped out using a spoon. However, the containers
of products such as tomato ketchup and salad cream have relatively narrow
openings. To cause these products to flow you first need to shake the
container quite vigorously. This 'shears' the liquid, 'breaking it up', so that
it can slip or flow more easily.
VISCOSITY AND INTERMOLECULAR FORCES
The viscosity of a liquid is due to the forces between its molecules-their
intermolecular forces. The stronger the forces hindering the motion of the
molecules, the greater the viscosity. (You may find it helpful to look back at
Unit 9 of S102 to familiarize yourself with this concept.)
Hydrogen bonding is particularly important in this respect because it can bind
neighbouring molecules together so strongly. This accounts for the fact that
water, for instance, has a greater viscosity than benzene (C6H6),in which there is
no hydrogen bonding. Glycerol (C3H7O3)is very viscous at room temperature
because of the numerous hydrogen bonds its molecules can form. Heavy
hydrocarbon oils, which are not hydrogen-bonded, are also viscous but their
viscosity arises partly because the long-chain molecules get tangled together,
like a plate of cooked spaghetti.
In the development of your new shower gel product viscosity is a critical
property that you will need to consider. When you have decided on an appropriate
'thickness' for your gel, you will need to make sure its viscosity is appropriate
for the container.
0
Can you suggest reasons why it is so important to ensure that the viscosity
is suitable?
H If the viscosity of the gel is too low then it will pour out of the container
too quickly; if the viscosity is too high the gel will not come out of the
container at all.
0 Are there any other considerations that you need to take into account
regarding the viscosity of the gel?
H The gel has to maintain its viscosity over quite a large range of
temperatures-possibly from freezing point in winter (0 "C) to over 25 "C
in summer, and when in use to a temperature of around 37 'C.
0 Viscosities of most liquids decrease with increasing temperature. Can you
suggest why this happens?
H At high temperatures the molecules have more energy and can move past
their neighbours more. readily. For example, the viscosity of water at
100 "C is one-sixth its viscosity at 0 'C-in
other words, the same amount
of water flows through a tube six times as fast at the higher temperature.
You can probably think of other common examples where this relationship
applies.
J
Some products may be at their thickest at room temperature. If the
manufacturing route involves a heating stage, odd results may be found if tests
are done before the products are cool. Likewise, products left on a cold
windowsill will show different properties from others stored by a radiator.
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
ACTIVITY 2: DESIGN OF GEL CONTAINERS
You will need:
,
a collection of empty shower gel containers
Examine a variety of shower gel containers, and discuss how the
manufacturers have dealt with the viscosity of the different gels.
Do you think that the viscosities of commercial shower gels differ from each
other? Activity 3 asks you to design and carry out an experiment to measure the
viscosity of some commercial gels.
/
1
ACTIVITY 3: MEASURING SHOWER GEL
VISCOSITY
You will need:
three or four commercial gel products
everyday equipment with which to make a comparative measure of viscosity,
for example a watch, small containers, tubing, funnel
Using samples of commercial gels, can you predict whether their viscosities
(or thicknesses) will be the same or different? How can you find out which
one is the thickest (that is, which has the highest viscosity)? Using your
everyday equipment, design an experiment to measure the relative viscosities
of the sample gels.
Make sure you are happy with the method of measuring that you dev"e1op in this
Activity; you will be using it again when you come to make your own gel in
Activity 4.
Viscosity can be measured by observing how long it takes a given volume of
liquid to flow through a narrow tube. A liquid with high viscosity (such as
treacle or molasses at room temperature) is said to be viscous.
Simple tests to make a comparative measure of viscosity include:
will the substance in question pour?
what does it look like when it is stirred?
what diameter pipe will it flow through?
how long does it take to flow through a tube?
how fast does a particular object (such as a ball-bearing) fall through a given
depth of the substance?
what is the diameter of one squirt of the substance on a particular surface?
You may have used one of these methods in your experiment in Activity 3.
Some of these tests do not fully characterize the viscosity; in fact some, like the
'blob' test, have more to do with other characteristics, such as surface tension
and adhesion.
Having established the viscosity of a commercial gel, you are now in a position
to manufacture your own gel from a given basic mixture.
Before you begin Activity 4, take a little time to think about:
the variables involved
the environment and conditions in which you are working
SCIENCE FOR PRIMARY TEACHERS
what data you are going to collect (for example, how many readings will
you make?)
the method you will use to record your results (you may find it helpful to
refer back to Unit 4 of S 102).
ACTIVITY 4: MANUFACTURE OF A SHOWER
GEL
The basic mixture of a shower gel comprises:
surfactant and CO-surfactant-these are the cleaning agents: the
surfactant causes the lather, and the CO-surfactantprevents too much
lather forming (you will learn more about surfactants in Section 4)
pH adjuster (citric acid solution)-body
give a pH of between 6.5 and 7
salt (sodium chloride)-this
products need to be adjusted to
is used as a thickening agent in detergents
preservative (usually formaldehyde)
water (deionized)-to dilute the basic mixture.
Your tasks are: (a) to develop a method of making and testing gels from a
given formulation, optimizing the amount of salt required to produce the
required viscosity; (b) to finalize the details of the gel product, which includes
deciding on its colour and perfume; and (c) to research and develop a
marketing campaign for your product.
Before you begin to make the gel you need to plan carefully how you will do
it. Use the method of measuring viscosity that you developed with the
commercial gel. If you need to modify the method in any way, think about
how to do this now.
The best way of making a batch of gel is in a container or glass beaker,
using a simple stirrer, such as a lollipop-stick. For initial experiments,
samples can be made either in a test-tube or in a small beaker, provided the
weighing is accurate. From this, the most promising formulations can be
found for manufacture on a larger scale.
A basic.gel formulation for testing can be made simply by using surfactant,
CO-surfactant,water and salt. At this stage do not worry about pH adjuster or
preservative. You need to make up a basic formulation of, say, 100cm3.
This formulation should consist of 13% surfactant, 2% CO-surfactant,with
the remainder-being made up of deionized water. To this is added a small
amount of salt to obtain a gel of the required viscosity.
To make the gel, first mix the surfactant and CO-surfactanttogether, then add
the water and stir. Measure the viscosity of this mixture. The product can
now be thickened by the addition of salt. To determine the optimum amount
of salt, divide up the batch (minus salt) intojive equal volumes. Now add the
following amounts of salt to your samples: 2 g; 4 g; 6 g; 8 g; 10 g. After
adding the salt, stir the solution until all the salt has dissolved. (Hint: Stir
gently until all the salt has dissolved. Stirring too vigorously will produce
excessive amounts of foam!)
Measure and record the viscosity for each sample. At this stage you can use
solid salt to establish the optimum amount, but once this is known, it is
better to use a salt solution to avoid areas of high salt concentration.
Your results can be recorded graphically, and you should be able to use them
to estimate the optimum amount of salt needed to produce the required
viscosity.
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
0 As you continued to add salt to the mixture, what did you notice about its
viscosity?
You should have noticed that the increase in viscosity can be quite sudden: a
little less than 3% salt by mass should give about the right viscosityabove this level the viscosity will start to reduce again. The reasons for this
are explained in Section 4.
Now that you have established the optimum amount of salt for your gel, you
need to consider two other factors. All commercial shower gels also contain a
colouring agent and some perfume (even those that are marketed as 'natural').
1 ACTIVITY 5:
I
1
FINALIZING THE PRODUCT
You will need:
your shower gel product
various food colourings
perfumed oils
Using different colours and perfumes, add very small quantities of (a) colour
and (b) perfume to your gel. Consult the marketing department before
making the final decision on colour and perfume.
You will need to test that the viscosity of the gel is not appreciably altered
by the addition of colour or perfume; adjust the amount of salt if necessary.
You may also wish to try measuring the pH of the product at this point.
The research department is responsible for developing the shower gel. However,
it cannot work in isolation. Since the product needs to be a commercial success
it has to meet customer demands, and the research and development section of the
company needs to know these requirements before finalizing the formulation of
the product. Input from other departments can be considerable.
ACTIVITY 6: MARKETING THE PRODUCT
1
1
1
/
Using the list below as a checklist, decide which areas you will continue to
research before releasing the product on to the market:
colour of product
perfume of product
design of container
packaging of container
I
advertisement designs
I
market research of people, shops, etc.
cost of product.
I Whatproposed
methods would you use to research into these areas?
1 ACTIVITY 7:
EVALUATION
Evaluate what you have achieved in terms of exploration skills and crosscumcular activities.
I
How could you develop this material for class use?
SCIENCE FOR PRIMARY TEACHERS
3 THE HISTORY OF SOAPS AND
DETERGENTS
WHY USE SOAPS AND DETERGENTS?
Ever since people started to use material and wear clothes they have needed to be
able to clean them. Not only do dirty clothes look shabby, but the grime in
them can harbour disease; it was a trunk of imported cloth containing infected
fleas that brought the Black Death to England in the 14th century.
One of the most primitive ways to clean clothes is to soak them in water. It was
found that this method worked better if the materials were agitated or beaten with
rocks. Certain plants, such as soapwort, have leaves that produce saponins,
chemical compounds that give a soapy lather. These were probably the first
'detergents' that people used. In Roman times, it was discovered that adding
alkaline substances to the washing water helped to clean the clothes. An alkali
called natrum found in Egyptian lakes and used to preserve mummies was also
used in washing. In the past, sailors have used urine, which contains another
alkali, ammonium carbonate, to wash their clothes.
There is no clear evidence about when soap was first invented, although it
certainly existed by AD 150. Soap is formed when vegetable oil or animal fat is
heated together with an alkali, and it may well be that discovery of soap was
accidental. The first people to make and export soap were the Arabs, some time
between 0 and AD 800. The first mention of soap-making in Britain was in
about AD 1000. People in northern Europe made soap from animal fat and fish
oil, while in southern Europe olive oil was used.
SOAP-AN
EXPENSIVE LUXURY
Early soap was expensive because it was heavily taxed. In soap factories the pans
used for heating the fat with alkali had lockable lids, and each night, excise men
would lock the pans so that illegal soap could not be manufactured. When soap
was expensive, it was not usual to wash one's clothes or body at all frequently;
much more reliance was placed on pomanders and scent. A popular view in the
18th century was that once a year was often enough for a bath. It was not until
the abolition of the soap tax in 1853 led to a reduction in the price of soap that
more interest was shown in personal cleanliness.
SOAP FOR ALL
The scientific breakthrough that led to the wider availability of soap was made in
1790, when Nicolas Leblanc discovered a way of making the alkali sodium
carbonate from common salt on a large scale. This meant that more soap was
manufactured, but it was still, on the whole, an unpleasant-smelling product
made from animal fat. Any fat that did not react with the alkali would eventually
turn rancid on exposure to air, and any alkali left in the product was harmful to
skin and fabric. This poor-quality soap was sold by the grocer in a large block; it
was very hard and produced little lather.
In Victorian times, washing clothes was heavy, time-consuming work. To get
clothes clean it was necessary to use boiling water. But in 1884, W. H. Lever,
son of a wholesale grocer from Bolton, introduced Sunlight soap. This product
was made from vegetable oils, lathered well and carried a guarantee of purity.
From this time the soap industry developed rapidly, producing specialized soaps,
such as Lifebuoy, which contained the disinfectant carbolic acid.
-.
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
SOAPLESS DETERGENTS-TODAY'S
ALTERNATIVE
Because of several disadvantages associated with the use of soap (which will be
discussed in Section 4) scientists developed a new type of cleaning agentdetergents. These were initially made from coal tar, but after the Second World
War increasing use was made of the new products of the petrochemical industry.
Crude oil was distilled to give mixtures of different chemicals. One of these
mixtures reacted with a concentrated acid to give a soap-like product. These
soapless detergents are now widely used.
A typical washing powder contains 'builders' and 'improvers' as well as
surfactant-take a look at the contents listed on a box of washing powder.
Builders help to soften the water as well as adding bulk to the detergent.
Improvers help the detergent to remove the dirt. Other chemicals in a washing
powder may include bleachers, brighteners and biological enzymes.
Unfortunately, although improving on soap in many ways, soapless detergents
have caused several environmental problems. These problems, and how the
detergent industry is trying to overcome them, will be discussed in Section 4.
We conclude this Section with a couple of Activities that you might like to try
out in the classroom.
ACTIVITY 8: KEEPING CLEAN
l Get the children to design and make two contrasting posters: one
showing how people have kept themselves and their clothes clean in the past,
and the other showing the products that we have available to us today for
keeping clean.
2 Find out whether the children know that there are two main types of
cleansilig agents: soaps and soapless detergents. Do they know in what ways
the two are different? Again, they could prepare posters showing the different
types, perhaps indicating advantages and disadvantages of each.
3 Get the children to devise an investigation to answer the question: 'Do
all detergents produce the same amount of lather?'
Note: The simplest test for lather is to shake a known volume of water with
a known volume of product for a j x e d time and then measure the height of
the foam. Other tests can be devised by washing with the products (wearing
rubber gloves) and making qualitative assessments of the lather rate and type.
ACTIVITY 9: EVERYDAY DIRT
I
Ask the children to make a list of all the stains their clothes might
accumulate during 24 hours.
4 THE CHEMISTRY OF SOAPS
AND DETERGENTS
WHAT ARE SOAPS AND DETERGENTS?
Ordinary soaps are the sodium salts of long-chain fatty acids. Their general
formula is RCOO-Na', where R is a long hydrocarbon chain, CH3(CH2)10-16
These salts can be made by the simple neutralization reaction:
SCIENCE FOR PRIMARY TEACHERS
0
R-<
II
-OH
+ NaOH- -b
acid
R-C
base
R-0-Naf
salt
+ H20
water
The cheapest sources of fatty acids are animal fats and certain vegetable oils,
which are usually esters. In practice, therefore, soaps are made by the
saponification reaction:
RA-0 - R' + NaOH
ester
(fat)
,
-
base
(caustic soda)
b R-C
- 0 - ~ a + + R' OH
salt or fatty acid
alcohol
(soap)
(e.g. glycerol)
Beef tallow gives sodium stearate, CH3(CH2),6COO-Na+,the most common
soap. Palm oil gives sodium palmitate, CH3(CH2),,COO-Na+, a component in
more expensive soaps. You have already come across these in 'The chemistry of
carbon compounds'. If the sodium ion of ordinary soap is replaced by other metal
ions, soaps with different properties are produced. When potassium hydroxide is
used instead of sodium hydroxide in the manufacturing process, soft soaps are
formed. These are semi-solid soaps, once used in shampoos and special-purpose
soaps.
Today, for many purposes, soap has been displaced by newer detergents. Why do
you think this has this come about? In some ways, ordinary soaps are better than
the newer detergents. They are relatively cheap and manufactured from a
renewable source-whereas many of the synthetic detergents are made from
petrochemicals. Soaps are also biodegradable-that is, they are readily broken
down by bacteria and so do not pollute rivers.
On the other hand, soap has a number of disadvantages: it deteriorates with time;
it lacks cleaning power when compared with the modern synthetic detergents,
which can be designed to perform specialized cleaning tasks; and it does not rinse
out easily, tending to leave residues behind in the fabric that is being washed.
These residues gradually build up and cause a bad odour, deterioration of the
fabric and other problems.
However, the most important reason for the displacement of soap is that it does
not easily produce a lather in hard water (water that contains certain dissolved
salts). Instead, a grey scum forms, which is wasteful of soap and spoils the
texture of garments. This scum is the result of a precipitation reaction that
ions in water react with sodium salts (soap) to give
occurs when ca2+or
less-soluble products.
The development of the first detergents in an effort to overcome the reaction of
soaps with hard water provides a good illustration of one of the standard
scientific approaches. If a useful substance has some undesirable property, an
attempt is made to prepare an analogue-a near chemical relation-that will
prove more satisfactory.
Soap is a su$actant-that
is, a surface-active cleaning agent. Modem commercial
detergents are mixtures of compounds, the most important of which is the
surfactant. (Note: The word detergent means 'cleaning agent' and so, strictly
speaking, soap is just one particular type of detergent; the cleaning agents
commonly known as detergents should therefore really be called soapless
detergents. However, in the following discussion we shall follow common usage
and talk about detergents rather than soapless detergents.)
Surfactants are synthetic organic molecules. They have a water-loving head
group (called the polar part) and a water-hating tail group (the non-polar part). In
addition to a surfactant, a detergent will also contain a compound that adjusts the
acidity of the detergent solution, as well as additives in the mixture that
.
LEARNING AND TEACHING CHEMISTRY THROUGH TOPIC WORK
'fluoresce'-that
is, they absorb ultraviolet light and then give out visible
light-to give the impression of greater cleanliness. Advertising slogans have
capitalized on this 'whiter than white' effect.
The widespread use of detergents has, however, caused some pollution problems.
Some of the early synthetic detergents were found to be non-biodegradable, and
they accumulated in rivers, polluting the water. During the 1950s it was a
common sight to see a river covered with foam. This problem was largely
overcome when the manufacturers found that if the carbon chain were straight, as
in animal fats, rather than being branched, the detergent would be biodegradable.
Other environmental problems are associated with the various bleachers,
brighteners and biological enzymes that are added to enhance the performance of
many detergents. For example, certain phosphate additives upset the balance of
river life by acting as nutrients for algae, causing the algae to multiply and form
a green scum on the water. The detergent industry is continually trying to
develop alternatives to harmful additives in order to produce an effective detergent
that will not damage the environment.
HOW DO SOAPS AND DETERGENTS WORK?
ACTIVITY 10: WHAT CAN DETERGENTS DO?
You will need:
a small square of fabric
test-tubes
elastic band
dropping pipette
detergent solution
spatula
carbon powder
1 Take a square of fabric and stretch it tightly across the top of a test-tube
(or similar container) using an elastic band.
2 Using a dropping pipette, carefully place one drop of water on to the
stretched fabric.
What shape is the drop as it rests on the fabric?
3 Using the same pipette, place one drop of detergent solution on to the
stretched fabric.
Do you notice any difference between the behaviour of the two drops?
What can you conclude from this about the presence of detergent in water?
Can you suggest why this might be an advantage when washing clothes?
4 Now half fill a test-tube with water.
5 Add one spatula of carbon powder, put a stopper in the top of the testtube and shake for a few minutes.
What do you notice about the carbon powder particles after they have been
shaken with water?
What do the carbon powder particles represent in this simulation of washing?
Now repeat steps 4 and 5, but instead of water use detergent solution.
6 What effect does the detergent have on the carbon particles?
7 Why might this be helpful when washing clothes?
SCIENCE FOR PRIMARY TEACHERS
The action of soaps and detergents as cleansing agents is two-fold. They
emulsify oil and grease and they lower the surface tension of the water, as a
result of which the water wets things more effectively. Normally, if a small
amount of water is placed on the surface of a piece of fabric, the drops do not
soak in (see Figure la). This is because the molecules of water exert such strong
attractive forces on each other they tend to stay as close to one another as
possible. If a drop of soap or detergent solution is added to this water, the waterhating groups of the soap or detergent molecules try to keep away from the
water, and the water-loving parts are attracted to the water. Therefore a lot of the
soap or detergent molecules arrange themselves at the interface between the water
molecules and the surface of the fabric (see Figure lb). This in turn makes for
greater attractive forces between the detergent solution and the fabric than
between water alone and the fabric. So, the detergent solution spreads out and
wets the fabric.
fabric
> l > > > >
60606 06 06 06
water and detergent
fabric
FIGURE 1 (a) A water drop on a piece of fabric. (b) A drop of water mixed with
detergent; note that the solution spreads out over a wider area, wetting the fabric more
effectively.
When dirty fabric is agitated in water containing soap or soapless detergent,
either by hand or'in a washing machine, not only is greasy material emulsified
but also solid particles of dirt are loosened and removed.
MAKING THE SHOWER GEL
You have already learnt that surfactant molecules consist of two very different
parts: a water-loving, or polar part, and a water-hating, or non-polar, part. These
parts adsorb strongly at waterloil interfaces since the polar part can be surrounded
by water while the non-polar part resides in the oil. Solutions of highly active
surface molecules (that is, detergent solutions) exhibit unusual physical
properties. At some concentrations, surfactant molecules aggregate to form
structures known as micelles. In these aggregates the (water-hating) hydrocarbon
tails lie towards the centre, while the water-soluble polar ends are at the surface
of the micelle (see Figure 2).
Most surfactants form small micelles of approximately spherical or ellipsoidal
shape that contain roughly 40 to 200 molecules. However, if the solution's
conditions, such as pH, temperature or electrolyte concentration, change, then
the size and shape of the micelles are altered.
FIGURE 2 A surfactant micelle.
Thus surfactants can cluster into a variety of structures in aqueous solutionsand these can transform from one to another as the solution's conditions change.
Adding salt to your basic shower gel formulation changes the structure of the
micelles. The higher the viscosity, the larger is the structure. As you continue to
add salt, the structure becomes unstable and breaks down. This has the visible
effect of reducing the viscosity of the solution-which you can measure.
5 THE WAY FORWARD
Using a topic approach, as we have done here, enables different concepts to be
introduced and reinforced; however, as you should now be well aware, careful
preparation and planning are essential to a successful outcome.
Much of the work you have covered in Science for Primary Teachers has focused
on one specific area at a time, but many of you will be teaching mainly through
topic work. 'Clean science', like 'Fuels' and 'Materials', offers you the
opportunity to tackle a complete topic, and think carefully about how you will
deal with the science content within it. This approach reflects our everyday
experience: no one problem exists in isolation; there are always a multitude of
factors to take into consideration.
It may be useful for you to spend some time now evaluating the benefits and
problems of teaching through cross-cumcular topic work.
SCIENCE FOR PRIMARY TEACHERS
RESOURCES
Harlen, W., Macro, C., Schilling, M., Malvern, D. and Reed, K. (1990)
Progress in Primary Science: Workshop Materials for Teacher Education,
Routledge.
Russell, T., Longden, K. and McGuigan, L. (1991) Primary SPACE Project
Research Report: Materials, Liverpool University Press.
Selinger, B. (1989) Chemistry in the Marketplace, Harcourt Brace Jovanovitch.
ACKNOWLEDGEMENTS
.
We are grateful to the Science in Primary'Teacher Education (SPRITE) Project
for their contribution to the 'Materials' topic.
We also wish to thank Unilever Research, Port Sunlight Laboratory, for their
help in the preparation of 'Clean science'.
NOTES
ISBN 0 7492 5032 1
THE OPEN UNIVERSITY