Gill
Science
Stage 4
S
Mixture separation
Part 3 – Making and separating mixtures
Number: 43922
Title: Mixture Separation
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Extract from Science Syllabus Years 7-10 © Board of Studies, NSW 2003
Overview
pp iii-iv
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Contents – Part 3
Lesson 11: Measuring volumes
3
Lesson 12: Making mixtures
9
Describing your observations
11
Solubility tests
14
Lesson 13: The solvent water
17
Different kinds of mixtures
21
Lesson 14: Some separation methods
23
Sieving
23
Decanting
27
Magnetic attraction
28
Evaporation
30
Lesson 15: Separating a mixture
33
Suggested answers – Part 3
37
Exercises – Part 3
41
Part 3: Making and separating mixtures
1
2
Mixture separation
Lesson 11: Measuring volumes
A mixture is something that contains any amounts of two or more
substances.
In your course you will often mix substances with water. To compare
mixtures of different substances with water you need to make sure that you
carry out fair tests.
A fair test is one where only one thing is allowed to change. The one thing
you change in this case is the type of substance. You don’t want to change
the amount of water and the amount of substance you use.
Amount can be the volume or mass of the substance. Scientists usually
measure the mass of the substance and water. If you don’t have the
equipment needed to measure mass accurately then measure the volume of
water and substance for each test.
How do you measure the volume of a liquid? This next activity will help
you to find out.
Activity: Measuring the volume of a liquid.
1
Name the piece of equipment that is used to measure the volume of a
liquid. _________________________________________________
A measuring cylinder is used to measure the volume of a liquid.
2
What is main unit used to record the volume of liquid? (Think about
how people buy liquids like milk or petrol).
_________________________________________________________
The usual unit of volume is a litre.
3
How do you write the abbreviation for litre?
_________________________________________________________
L is the abbreviation for litre. (L can also be called the symbol for litre.)
A litre is too much liquid to use in most experiments. It is often more
1
convenient to use a millilitre (
litre) to measure volumes. Use mL as
1000
the abbreviation for the unit, millilitre.
Part 3: Making and separating mixtures
3
Activity: Measuring volume using a measuring cylinder
Get a measuring cylinder and pour some water into it.
Now have a good look at the top surface of the liquid. You’ll need to put
your eyes level with the surface of the water in the container.
Which drawing below looks most like the top surface? _________________
The top surface of the water should look like drawing B.
Whenever water is put into a glass or plastic container, the edges of the top
surface curve up slightly. The curved surface is called the meniscus.
Other liquids also form a meniscus on their surface. Most liquids have a
meniscus that curves upwards. Mercury is an unusual liquid because it has a
meniscus that curves downwards (drawing C).
Where do you measure the volume of liquid? Always measure the volume
from the flat part of the meniscus. In the case of water, this is the bottom of
the meniscus. For mercury, this is the top of the meniscus.
What else do you have to remember
when you read scales? You have to
make sure that your eyes are level
with the scale and the thing you are
measuring.
To measure the volume of water,
your eyes have to be level with the
bottom of the meniscus.
Activity: Water level
Here is a drawing of a glass measuring cup. Draw what you would see when
the cup is half full of water.
4
Mixture separation
Check your drawing.
Activity: Reading the scale on a measuring cylinder
Look at the scale on the diagram of the measuring cylinder below.
1
What are the lowest and highest numbers on
the scale?
______________________________________
The lowest number on the scale is 10 and the
highest is 100.
2
What is the range of volumes that you can
measure with this measuring cylinder?
______________________________________
The range of volumes is from 10 mL to 100 mL.
The range is found using the lowest and highest
measurements that can be made.
Now let’s look more closely at the scale marks between two values: 10 mL
and 20 mL.
3
Find the line halfway between 10 and 20
on the scale. The number 15 is halfway
between 10 and 20, so this line must be 15.
Label it on the diagram.
4
How many spaces are between 10 and 15
on the scale? _______________________
Did you count five?
5
How many lines are there between 10 and 15? _________________
There are four lines.
Part 3: Making and separating mixtures
5
6
How many whole numbers are between 10 and
15? ___________________________________
Four again: 11,12,13 and 14. So, each line
represents a number.
7
Label the numbers on the scale.
8
Now fill in the numbers between 15 and 20.
Does your answer look like this?
You can’t write the numbers onto your measuring cylinder, but you can
always count up the lines if you remember what each line means. Each line
is called a scale mark or scale division. On this measuring cylinder, each
scale division represents 1 mL.
Activity: Practice using scales
What is the reading on each of these millilitre scales? Write the answer on
the line below each scale. Include the unit in each answer.
Check your answers.
6
Mixture separation
Now that you know what each scale division represents, you can read the
volume of liquid in a measuring cylinder.
Activity: Using a measuring cylinder to measure volume
Look at the meniscus of the water in the measuring cylinder.
1
What are the two scale numbers that the water level
lies between? ___________________________
The water levels lies between 70 and 80.
This means that the volume is greater than 70 mL but less
than 80 mL. Now you have to decide how much more
than 70 mL it is.
2
Count up from 70 and write down how many scale
marks there are between 70 mL and the water level.
Remember to look at the bottom of the meniscus to
find the value. _________________________
The water is level with the eighth mark above 70.
3
What is the volume of liquid in the measuring
cylinder? _______________________________
The volume of liquid is 70 + 8, or 78 mL.
Activity: Using a measuring cylinder to measure volume
Look at the meniscus of the water in the measuring cylinder. Write the
meniscus on the line below the diagram.
The meniscus is:
Part 3: Making and separating mixtures
The meniscus is:
7
Check your answers.
The scales on beakers are not accurate and should never be used to measure
a volume. They are useful for rough estimates only.
Volumes of solids
It is not easy to measure the volume of a solid. We’ll try to use small
amounts of solid so that it is easy to see what happens to the solid. Teachers
often talk about small amounts of solids as ’rice grains’ of solids.
This is the size of an uncooked a rice grain. This is the amount of solid
you should use for each test.
Complete Exercise 3.1: Using a measuring cylinder.
8
Mixture separation
Lesson 12: Making mixtures
What happens when substances are mixed with water? Let’s do some tests
and find out.
Activity: Mixtures with water
What you will need:
•
very clean test tube
•
table salt
•
ground pepper
•
flour
•
sand
•
teaspoon
•
measuring cylinder.
Please make sure that your glassware is very clean. You will taste some
chemicals in this experiment.
What you should do:
1
Use your measuring cylinder to measure out 10 mL of water. Pour the
water into a test tube.
2 Add one rice grain
volume of table salt to
the water. You might find
this easier to measure out
if you use the handle end
of your teaspoon
3 Shake the test tube. Do
this by holding it loosely
between the fingers and
thumb of one hand and
tapping it with the fingers
of your other hand.
Shaking a test tube safely
Part 3: Making and separating mixtures
9
4
Tick the sentence that match your observation.
The salt sank to the bottom of the test tube.
The salt disappeared.
The salt spread out through the water.
The salt floated.
Your answer should be ’The salt disappeared.’ Answer the questions
following.
1
Has the salt really disappeared? Write down where you think the salt is
now.
_________________________________________________________
2
How can you test your idea?
_________________________________________________________
You can taste the water to find out if the salt has disappeared.
3
What did you find out when you carried out your test?
_________________________________________________________
The water tasted salty.
The salt you added is still in the test tube, but you cannot see it any more.
The mixture of salt and water is clear, you can see straight through it.
Now try pepper. Rinse out the test tube and measure another 10 mL of
water. Put a rice grain volume of pepper into the water in the test tube. Tick
the sentence that best describes what you observe.
The pepper sank to the bottom of the test tube.
The pepper disappeared.
The pepper spread out through the water.
The pepper floated.
Did you notice that the pepper floated?
Now test a rice grain volume of flour in the same way. Again record your
observation by ticking one of the sentences.
The flour sank to the bottom of the test tube.
The flour disappeared.
10
Mixture separation
The flour spread out through the water.
The flour floated.
Did you see that the flour spread out through the water? If you leave the test
tube without shaking it for some time, you will find that the flour sinks to
the bottom of the test tube.
Put a rice grain volume of sand in 10 mL of water, shake the mixture and
observe what happens. Tick one sentence to describe your observations.
The sand sank to the bottom of the test tube.
The sand disappeared.
The sand spread out through the water.
The sand floated.
Did you notice that the sand sank to the bottom of the test tube?
Summarise your results by writing the names of the substances you tested in
the spaces in these sentences.
The _________________ disappeared when mixed with water.
The _________________ floated on the surface.
The _________________ spread out through the water.
The _________________ sank to the bottom.
Check your answers.
Describing your observations
Activity: Describing your observations of mixtures
Salt and water
Read this description of an experiment.
I placed the salt in the water. The salt disappeared and made salty water.
Salt mixes with water.
Now read this second description of the same experiment.
The solute, salt, was placed in the solvent, water. The salt dissolved and
formed a solution, salty water. Salt is soluble in water.
Part 3: Making and separating mixtures
11
Which word or words in the second description do you think means:
a
the solid part of the mixture? _________________________
b
the liquid part of the mixture? ________________________
c
disappeared? ______________________________________
d
the mixture that was formed? _________________________
e
dissolves? ________________________________________
Here are the answers. Please check them carefully.
a solute
b solvent
d solution
e is soluble
c dissolved
Sugar behaves in the same way as salt when it is mixed with water. Fill in
the blank spaces in these sentences describing what happens. Use the words
below to fill in the spaces. Each word is used once.
solution
dissolves
soluble
solvent
solute
When sugar is mixed with water, the sugar disappears. Another way of
saying this is that the sugar _______________ in the water, or that sugar is
_______________ in water. The sugar is the _______________ and the
water is the _______________. The mixture that is formed is called a
_______________.
When sugar is mixed with water, the sugar disappears. Another way of
saying this is that the sugar dissolves in the water or that sugar is soluble in
water. The sugar is the solute and the water is the solvent. The mixture that
is formed is called a solution.
Solutions in water are called aqueous solutions or aqueous mixtures. The
word aqueous refers to water. If you are reading about a solution, for
example a sugar solution, and no solvent is indicated then assume that the
solvent is water. Assume that it is an aqueous sugar solution.
Pepper and water
Does pepper dissolve in the water? ______________________
Is pepper soluble in water? ____________________________
Pepper does not dissolve in water. It is not soluble in water.
These are some ways we can say that a substance either floats or sinks to the
bottom of water.
12
•
The substance is not soluble in water.
•
The substance is insoluble in water.
•
The substance does not dissolve in water.
Mixture separation
Use one of these phrases to write a sentence to describe what happened
when you mixed pepper with water.
_____________________________________________________________
_____________________________________________________________
Your sentence should match one of the sentences below.
•
The pepper is not soluble in water.
•
The pepper is insoluble in water.
•
The pepper does not dissolve in water.
Flour and water
Some substances spread through the liquid but they do not dissolve. What is
formed is called a suspension. The flour formed a suspension with water.
The flour was suspended in the water. (Suspend means hang. By saying this
you are saying that the flour hangs in the water.)
Sand and water
The sand sank to the bottom of the test tube. The sand forms a sediment.
After some time, the flour also forms a sediment.
Summary of your results
Fill in the name of one of the substances you tested in each space.
The ___________________ formed a sediment when mixed with water
The ___________________ formed a suspension when mixed with water.
The ___________________ floated when mixed with water.
The ___________________ formed a solution when mixed with water.
Check your answers.
Part 3: Making and separating mixtures
13
Solubility tests
Solubility is whether a substance dissolves or not. It is a property of each
substance.
Activity: Testing water solubility of substances
You will need to collect at least four substances from home for testing. Here
are some suggestions of things you can test.
From your kitchen:
•
a powder cleaner
•
custard powder
•
powdered milk
•
cocoa.
From your bathroom:
•
talcum powder
•
soap
From your laundry:
•
washing powder.
From your gardening equipment:
•
lime
•
fertilisers
Testing substances
What you will need:
•
4 test tubes or 4 old jars
•
teaspoon
•
beaker
•
measuring cylinder
•
4 solids to test.
Remember – no tasting!
14
Mixture separation
What you should do:
1
Stand your test tubes in the beaker. Use your measuring cylinder to add
10 mL of water to each test tube.
2
Write the name of the first substance in the left-hand column of the
table below. Take a rice grain of the substance. Put it in the test tube
and shake the test tube.
3
Put the test tube back in the beaker and observe what happens.
4
Record your observation in the table next to the name of the substance.
5
Do the same for the other three substances.
Solubility of various household substances in water
Name of substance
What happens when it is placed in water?
Complete Exercise 3.2: Solubility tests
Part 3: Making and separating mixtures
15
16
Mixture separation
Lesson 13: The solvent water
Earth is the only water-rich planet in the Solar System. The colour of Earth
from space is due to water: the blue colour of thick layers of water in the
seas; the white reflection of sunlight from ice crystals and water droplets in
clouds; the brown landscape shaped by water; and the green of water rich
plants.
Water is the only chemical found as a solid, liquid or gas wherever living
things are found. Because many chemicals dissolve in water, most water on
Earth, like sea water, is a mixture.
Here are some hints to help you understand more as you read the next
activity.
1
Read the passage quickly. This should give you an idea about the things
mentioned in the passage.
2
Read the questions after the passage. These are the questions that you
will answer on your send-in page.
3
Read the passage again. This time read slowly and carefully.
4
Start answering the questions. By now you should have a good idea
where the answers can be found in the passage.
5
Write your answers roughly in the space provided. Your answers do not
have to be in sentences at this stage.
6
Check that you have answered the question you were asked. Students
often copy words from a passage that are related to, but do not answer,
the question.
7
Transfer your answers to your send-in page. Your send-in answers must
be in sentences.
Activity: Comprehension exercise on the solvent water
Read the passage and then answer the questions.
The solvent water
One of the great goals of the early chemists was to find the ’universal
solvent’ or a liquid that would dissolve everything. Many people thought
that the universal solvent was water because it was so common.
Part 3: Making and separating mixtures
17
Water will dissolve many substances, but not all. However, water is
certainly a very important solvent.
Living things depend on substances that dissolve in water. The oxygen
dissolved in water enables fish to ’breathe’. About 70% of your body
mass is made of water solutions. The most common solvent in your body
is water.
However, fats and oils in your body also act as solvents. Some of the
vitamins and hormones (chemical messengers) in your body are soluble in
oil, not water. Some pesticides (chemicals which kill insects) have been
banned because they dissolve in the fat in our bodies and can harm us.
Mothers breastfeeding their babies passed on the pesticide to the baby.
Solutions are important in the non-living parts of our world too. The gas
carbon dioxide dissolves in water. The water in the oceans helps to
remove this greenhouse gas from the atmosphere. Caves form because
water containing dissolved carbon dioxide slowly dissolves limestone.
Other gases in the atmosphere can also dissolve in water. Some pollutants
dissolved in water form acid rain.
But many things do not dissolve in water. For example, grease, kerosene
and starch are insoluble in water. Starch seems to dissolve, but really only
forms a suspension and sinks to the bottom if it is left to stand. Many
medicines are suspensions of substances in water. You can easily tell
which ones as they are labelled, ’shake well before using’.
How can we dissolve things that are not soluble in water? We can try
other solvents. Grease can be removed from clothing using dry cleaning
liquids. Oil paint brushes can be washed in mineral turpentine. Some
metals react with acids to make solutions.
Is there a solvent for every substance? No single acid will dissolve silver
or gold, but a mixture of very strong acids can. Glass will dissolve in an
acid called hydrofluoric acid. This acid cannot be kept in a glass bottle.
Chemists try to find solvents for all substances.
Not only do chemists try to find solvents for everything, they also try to
find substances that do not dissolve in anything. Teflon is used as the
surface of non-stick cookware. It has no known solvent. Teflon is tough,
strong and does not seem to react with anything.
Did you read the passage carefully? If you did, you should be able to answer
these questions. The answers for all these questions are in the passage.
1
Name two substances that will dissolve in water.
_________________________________________________________
_________________________________________________________
2
Name two substances that will not dissolve in water.
_________________________________________________________
_________________________________________________________
18
Mixture separation
3
Give one example of how living things depend on solutions.
_________________________________________________________
_________________________________________________________
4
Give one example of how solutions affect the non-living environment.
_________________________________________________________
_________________________________________________________
5
Would you try to remove grease from clothing using water only?
Explain your answer.
_________________________________________________________
_________________________________________________________
6
Do you agree that water is an important solvent? Why or why not?
_________________________________________________________
_________________________________________________________
Use your answers to help you complete the next exercise.
Complete Exercise 3.3: Comprehension exercise on the solvent water.
Activity: Test on water mixtures
The photograph below shows what happened when two substances were
mixed with water.
1
Which beaker contains the suspension? How can you tell?
_________________________________________________________
_________________________________________________________
Part 3: Making and separating mixtures
19
2
The solid being put into the water dissolves in water.
a
Complete the labels on the diagram.
b
What is another way of saying ’the solid dissolves in water’?
______________________________________________________
______________________________________________________
c
How could the student tell that the solid dissolves in water? What
observation would he make?
______________________________________________________
______________________________________________________
3
Read this description of an experiment. When you have finished, select
a word or phrase from the list to replace the ones that are underlined in
the each sentence. Re-write the sentence using this word on the line
underneath. Here is the list of words and phrases you should use.
solute
forms a suspension
sediment
solvent
dissolved
floats on
is insoluble
solution
When I put some salt in the water, the salt disappeared.
_________________________________________________________
The water is the thing that did the dissolving.
_________________________________________________________
The thing that dissolved was the salt.
_________________________________________________________
Salt dissolved in water to form a clear liquid.
_________________________________________________________
20
Mixture separation
Pepper does not disappear when it is placed in water.
_________________________________________________________
The pepper forms a layer on top of the water.
_________________________________________________________
Sand does not dissolve in water either. It forms a layer at the bottom of
the water.
_________________________________________________________
I also found that flour did not dissolve in water. It spreads itself
throughout the water.
_________________________________________________________
Check your answers.
Different kinds of mixtures
How many different kinds of mixtures do you think there are? Let’s look at
some mixtures that have two parts.
There are three states of matter that can be combined to make mixtures.
Write down all the possible combinations of the three states of matter to
form a mixture with two parts. (There are six possible combinations.)
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
Part 3: Making and separating mixtures
21
Tick off your answers on this list. Here are all the possible combinations:
a solid and a liquid
a gas and a solid
both solids
both liquids
a gas and a liquid
both gases.
What kind of mixture is air? (What states of matter are in air?)
_____________________________________________________________
Air is a mixture of gases.
How would you describe rocks?
_____________________________________________________________
Rocks are mixtures of solids. (Why? Minerals are the basic building blocks
of rocks, and minerals are solids.)
22
Mixture separation
Lesson 14: Some separation methods
In this lesson you will find out about four ways to separate mixtures:
sieving, decanting, magnetic attraction and evaporation.
Sieving
How difficult is it to separate the parts of a mixture? This next activity looks
at different mixtures and separating methods.
Activity: Sieving
A mixture of beans and rice
1
The photograph above shows a mixture of beans and rice. How would
you separate this type of mixture?
_________________________________________________________
It would be easy to pick out the beans because they are a different size
from the rice grains.
Part 3: Making and separating mixtures
23
A mixture of coins
2
What about a mixture of coins? How would you separate them?
_________________________________________________________
You could sort out the coins by hand, as long as there were not too
many of them.
3
What property of the coins would you be using to separate them?
_________________________________________________________
You might look at the colours and patterns on the coins, but you’d
probably concentrate on the different sizes.
In banks the coins are allowed to pass through a series of different sized
holes. All the coins, except 50c coins, can pass through the largest holes.
This separates the 50c coins from all the others. The next sized holes let all
the rest of the coins through except 20c coins. The next set of holes
separates $1 coins from the rest. Eventually, all the coins are sorted by size.
4
Can you think of something in your kitchen that allows some things to
pass through a series of holes, but prevent other things from passing?
_________________________________________________________
A colander, strainer or tea strainer does the same job as a coin sorter.
Coin sorters and strainers in the kitchen are examples of sieves. A sieve is a
piece of equipment that has a series of holes in it. The holes let some objects
pass through but not others. Later you will use a type of sieve with holes
that are too small to see.
24
Mixture separation
Below is a picture of a mixture of four different sized balls. Use this picture
to answer the questions about sieving in the next activity.
Activity: Using a model of a sieve
1
Use your ruler to measure the
diameter of each ball in millimetres
(mm).
Diameter of Ball 1
Diameter of Ball 2
Diameter of Ball 3
Diameter of Ball 4
Here are four sieves. Measure the opening in each sieve in millimetres.
Do that by measuring from side to
side across the square and not along
the diagonal.
Opening in Sieve 1 = _________
Part 3: Making and separating mixtures
Opening in Sieve 2 = __________
25
Opening in Sieve 3 = _________
Opening in Sieve 4 = __________
Check your measurements in the suggested answers before you begin the
next questions.
The solid balls have been mixed into some water to make them easier to
separate. None of the balls dissolve in water.
Use your measurements of the balls and the sieves to help you answer these
questions.
2
Which sieve could be used to separate all the solid balls from water?
_________________________________________________________
3
Which is the smallest sieve that will separate Ball 1 from Ball 4?
_________________________________________________________
4
What is the largest sieve that can be used to separate Ball 1 from Ball 4?
_________________________________________________________
5
Which sieve can be used to separate Ball 2 from Ball 3?
_________________________________________________________
6
Which sieve will separate Ball 1 from the rest of the balls?
_________________________________________________________
Check your answers.
26
Mixture separation
Decanting
Suppose you had a mixture of sand and water. You could sieve the sand out
of the water if you had a sieve with very small holes. What is another way
that you could separate the sand from the water?
Did you think that you could carefully pour the water out and leave the sand
behind? Pouring off a liquid and leaving a solid behind is called decanting.
Activity: Decanting
1
What sort of mixtures would you use decanting to separate?
_________________________________________________________
Decanting is useful for separating an insoluble solid sediment from a
liquid.
2
Imagine you are boiling water in a container over a fire and add tea.
How do you pour a cup of tea without getting any tea leaves in the pot.
_________________________________________________________
Decant it! Carefully pour out the tea so that the leaves stay in the
container. (The tea leaves are the sediment and the tea is the liquid.)
Water treatments between a dam or reservoir and your home
Part 3: Making and separating mixtures
27
Decanting can separate mixtures where a solid is insoluble in a liquid.
Activity: Using sieving and decanting on our drinking water
Use the information on water treatment in the picture on the previous page
to answer the questions following.
1
How many times is the water decanted?
_________________________________________________________
2
In which step is the water sieved?
_________________________________________________________
3
How many times are things mixed with the water?
_________________________________________________________
Check your answers.
Magnetic attraction
What property is being used to separate the mixture of sand and iron filings
in the diagram below? (Iron filings are very small pieces of iron.)
Separating sand and iron filings
The property that is used is that iron filings are attracted to a magnet, but
sand is not. Iron filings are magnetic but sand is non-magnetic.
Activity: Magnetic attraction
Some steel pins and plastic buttons are mixed together. Could you use
magnetic attraction to sort them out? Explain your answer.
_____________________________________________________________
_____________________________________________________________
28
Mixture separation
Most pins are made of iron so they are magnetic. They will be attracted to a
magnet. The buttons will not be attracted to the magnet because they are
made of plastic. So, magnetic attraction will separate this mixture.
But some pins cannot be separated from plastic buttons. These pins are
made from brass. Brass pins are not attracted by a magnet. Magnetic
separation cannot be used to separate brass pins from plastic buttons.
Check your answer.
Magnetic attraction is a well-known technique for separating iron from other
scrap metal. It is also used to separate minerals. This technique is called
magnetic separation.
Beach sand often contains two minerals called rutile and ilmenite. Ilmenite
is magnetic, but rutile is not. In the next activity there is a diagram of the
machine that is used to perform the separation.
Separating rutile and ilmenite
Part 3: Making and separating mixtures
29
Activity: Using magnetic attraction on beach sand
In the diagram on the previous page, one container has rutile in it and the
other has ilmenite. Write the contents under each container.
Check your answers.
Evaporation
Evaporation is a very common way to separate many mixtures. How could
you separate sugar from a mixture of sugar and water? Here’s a hint about
how you might do it. The diagrams below show what happens when some
water is left in an open container.
Evaporation over time
Use this diagram to answer the questions in the next activity.
Activity: Evaporation
What do you notice about the level of water in the containers?
____________________________________________________________
The level of water is lower each day. (There is less water each day.)
The water level in the container drops because liquid water can evaporate or
turn into a gas. Eventually there would be no water left in the container. So
how would you get the water out of the sugar and leave the sugar behind?
_____________________________________________________________
Evaporate the water.
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Mixture separation
Evaporation occurs more quickly when the mixture is heated. To get the
sugar quickly, you could gently heat the sugar solution.
What sort of mixtures can be separated by evaporation?
_____________________________________________________________
Solutions are usually separated by evaporation, but the method will work for
any mixture of a solid and a liquid.
You have washed your shirt. How do you get it dry? (To dry your shirt you
have to separate the water from the fabric.)
_____________________________________________________________
You hang it up or put it in a dryer so that the water evaporates.
You will summarise these separation methods in the next activity.
Activity: Summarising separation methods
1
Complete the table below.
Summarising separation methods
Separation method
Type of mixture
sieving
magnetic attraction
decanting
evaporation
2
Draw a line to match each separation method with its description.
sieving
attracting iron or nickel towards a magnet
and leaving non-magnetic substances
behind
decanting
pouring a liquid off and leaving a solid
behind
magnetic attraction
turning a liquid into a gas and leaving
another substance behind
evaporation
using a series of holes to remove different
sized solids
Check your answers.
Part 3: Making and separating mixtures
31
Complete Exercise 3.4: Separation methods
32
Mixture separation
Lesson 15: Separating a mixture
One of the world’s most important methods of separating minerals from
rock was developed in Australia.
Broken Hill in western NSW has the largest deposit of zinc, lead and silver
minerals in the world. In the early 1900s waste rock from the mining
operations still contained up to 20% zinc. A lot of money could be made if a
method was developed to separate the zinc from the waste.
Mining companies developed a method called froth flotation to separate
zinc from waste. Crushed rock was mixed with water and air was bubbled
through the mixture. As bubbles floated to the top of the mixture mineral
crystals could attach to the rising air bubbles. A chemical added to the
mixture coated the zinc crystals and joined them to rising air bubbles. The
froth that floated to the top of the mixture was rich in zinc.
Where would the mining companies get chemists in Australia that knew
about making froth? Some of the chemists that helped develop the methods
of separating minerals by froth flotation had worked in breweries making
beer! Scientific concepts and principles used in making beer were applied to
the separation of minerals.
This next activity allows you to put your scientific knowledge about
separation methods into practice.
Activity: Separating a mixture
The four parts of the mixture are:
•
iron filings (very small pieces of iron)
•
marble chips (large white lumps of the rock, marble)
•
sand grains
•
salt crystals.
When you have separated the mixture, you will send the four parts to your
teacher, so make sure you don’t throw anything away!
What you will need:
•
a mixture containing iron, marble, sand, salt
•
magnet
Part 3: Making and separating mixtures
33
•
beaker
•
tripod
•
spirit burner
•
wire gauze
•
safety goggles
•
large glass jar
•
4 sheets of newspaper
•
plastic teaspoon
•
plastic wrap or a plastic bag
•
4 small plastic bags, or envelopes, or paper and sticky tape
•
hot water
•
matches.
Separating the iron filings
Please wrap your magnet in plastic
wrap or put it into a plastic bag before
you start this activity. This will keep
your magnet clean. If you get iron
filings on your magnet, they will be
very difficult to remove.
1
Tip the mixture onto a sheet of newspaper.
2
Hold the magnet under the newspaper and watch what happens to the
parts of the mixture.
3
Use the magnet to separate the iron filings from the rest of the mixture.
4
Put the iron filings in one of the small plastic bags or envelopes or wrap
them in a sheet of paper and seal the parcel with sticky tape. If you’ve
used an envelope or paper, label the sample as iron filings.
Complete Exercise 3.5a: Separating iron filings.
Can you suggest a way of removing another part from the mixture?
_____________________________________________________________
_____________________________________________________________
34
Mixture separation
The remaining parts of the mixture seem to have two different sized
particles. You can separate these easily by using a sieve. The sand grains
and salt crystals will pass through the sieve, but the marble chips will be
trapped by the sieve. You can use a wire gauze as a sieve, or you can use a
kitchen strainer or a tea strainer instead.
Separating marble chips
1
Spread out another sheet of newspaper and put the beaker in the centre.
Cover the beaker with the wire gauze or sieve. Carefully pour a little of
the mixture onto the sieve and tap it or shake it until all the small
particles have passed through it. Continue until you have separated all
the mixture.
2
Put the marble chips in another small plastic bag or envelope or wrap
them in paper and seal it with sticky tape. Label the parcel if you can’t
see the marble chips.
Complete Exercise 3.5b: Separating marble chips.
If you mix the sand and salt with water, what will happen to the salt?
_____________________________________________________________
If you mix the sand and salt with water, what will happen to the salt?
_____________________________________________________________
The salt will dissolve but the sand will not.
Separating the sand
1
Pour some hot water into the beaker containing the mixture of sand and
salt. The beaker should be about half-full with hot water. Gently stir the
mixture in the beaker with the teaspoon.
2
Leave the mixture to stand for a few minutes.
How can you separate the salty water from the sand?
_________________________________________________________
You can decant the salty water from the sand.
3
Get the glass jar. Slowly and carefully pour out the salty water leaving
the sand behind in the beaker.
Part 3: Making and separating mixtures
35
4
Spread out the sand on some newspaper and leave it in a warm place
until it is dry. Then put it in a small plastic bag or envelope or wrap it in
paper.
Do not put wet sand in the plastic bag or envelope.
Complete Exercise 3.5c: Separating sand.
Separating the salt
If you wish, you can leave your glass jar in a warm place until it is dry, or
you can use the method below.
Make sure you are wearing your safety goggles.
1
Clean the beaker and pour the salty water into it.
Do not use the glass jar to heat the solution.
2
To remove the water from the salty water quickly, put the beaker on a
tripod and gauze. Heat the beaker gently using a spirit burner. Stop
heating while there is still some water in the beaker. You could burn
yourself if the mixture spits.
3
Leave the beaker to cool and the last of the water will disappear.
4
Spread out the salt on some newspaper and leave it in a warm place
until it is dry. Then put it in a small plastic bag or envelope or wrap and
seal it in paper. Label your parcel of salt.
Do not put wet salt in the plastic bag or envelope.
Complete Exercise 3.5d: Separating salt.
36
Mixture separation
Suggested answers – Part 3
Activity: Water level
Activity: Practice using scales
15 mL
61 mL
36 mL
68 mL
Make sure that you have written the abbreviation for the unit millilitre, mL
after each measurement. This is a unit for measuring volume.
Activity: Using a measuring cylinder to measure volume
84 mL
35 mL
Activity: Mixtures with water
The salt disappeared when mixed with water.
The pepper floated on the surface.
The flour spread through the water.
The sand sank to the bottom.
Part 3: Making and separating mixtures
37
Activity: Describing your observations of mixtures
The sand formed a sediment when mixed with water.
The flour formed a suspension when mixed with water.
The pepper floated when mixed with water.
The salt formed a solution when mixed with water.
Activity: Tests on water mixtures
1
The beaker on the right contains the suspension. The particles ’hanging’
in the liquid stop you from seeing through a suspension. A solution lets
light pass through it.
2
a
b
c
3
The solid is soluble in water.
The student would observe that the solid disappeared and the
solution was clear.
When I put some salt in water, the salt dissolved.
The water is the solvent.
The solute was the salt.
Salt dissolved in water to form a solution
Pepper is insoluble in water.
The pepper floats on the water.
Sand does not dissolve in the water either. It forms a sediment.
I also found that flour did not dissolve in water. It forms a suspension.
38
Mixture separation
Activity: Using a model of a sieve
1
Diameter of Ball 1 = 15mm
Diameter of Ball 2 = 11 mm
Diameter of Ball 3 = 9 mm
Diameter of Ball 4 = 5 mm
2
Here are the sizes of the square holes in the sieves.
Opening in Sieve 1 = 13 mm
Opening in Sieve 2 = 10 mm
Opening in Sieve 3 = 7 mm
Opening in Sieve 4 = 3.5 mm
Check that you have include the unit millimetre (mm) in each answer
3
Sieve 4
4
Sieve 3
5
Sieve 1
6
Sieve 2
7
Sieve 1
Activity: Using sieving and decanting on our drinking water
1
The water is decanted three times: once from the reservoir, once after
Step 1 and again after Step 2.
2
The water is sieved in Step 3. (The sieve is the layers of sand and
gravel.)
3
Things are mixed with the water three times: chemicals in Step 2,
chlorine in Step 4 and air in Step 5.
Activity: Using magnetic attraction on beach sand
Part 3: Making and separating mixtures
39
Activity: Summarising separation methods
1
40
Separation method
Type of mixture
sieving
solids of different sizes
magnetic attraction
magnetic materials with non-magnetic materials
decanting
sediments with liquids
evaporation
solids with solutions
sieving
attracting iron or nickel towards a magnet
and leaving non-magnetic substances
behind
decanting
pouring a liquid off and leaving a solid
behind
magnetic attraction
turning a liquid into a gas and leaving
another substance behind
evaporation
using a series of holes to remove different
sized solids
Mixture separation
Exercises – Part 3
Exercises 3.1 to 3.5
Name ________________________________________________________
Teacher ______________________________________________________
Exercise 3.1: Using a measuring cylinder
1
Explain why you should use a measuring cylinder rather than a beaker
to measure volumes of liquids accurately.
_________________________________________________________
_________________________________________________________
_________________________________________________________
2
What is the volume of liquid in this measuring cylinder? ____________
Part 3: Making and separating mixtures
41
3
Write the volume to the nearest millilitre (mL) below each of these
measuring cylinders.
Volumes are ___________________________________
Volumes are ___________________________________
42
Mixture separation
Exercise 3.2: Solubility tests
Copy your results from Activity: Testing water solubility of substances into
the table below.
Solubility of some household substances in water
Name of the substance
What happens when it is placed in water?
Write a report for your teacher, describing the results of your solubility tests.
Your report should be in sentences.
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
Part 3: Making and separating mixtures
43
Exercise 3.3: Comprehension exercise on the solvent
water.
1
Name two substances that will dissolve in water.
_________________________________________________________
2
Name two substances that will not dissolve in water.
_________________________________________________________
3
Give one example of how living things depend on solutions.
_________________________________________________________
_________________________________________________________
4
Give one example of how solutions affect the non-living environment.
_________________________________________________________
_________________________________________________________
5
Would you try to remove grease from clothing using water only?
Explain your answer.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
6
Do you agree that water is an important solvent? Why or why not?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
44
Mixture separation
Exercise 3.4: Separation methods
In this exercise, you have to decide how to separate three different mixtures.
The table contains information about the physical properties of some
substances. You will use the information in the table to decide on the type of
mixture and which separation method to choose.
Physical properties of four substances
Substance
Physical properties
What happens
when it is placed
in water?
Colour and state
Magnetic or not
nickel
forms a sediment
grey solid
magnetic
sulfur
forms a suspension
yellow solid
not magnetic
water
–
colourless liquid
not magnetic
copper sulfate
dissolves
blue solid
not magnetic
The three mixtures are:
Mixture 1: a mixture of nickel and sulfur
Mixture 2: a mixture of copper sulfate and water
Mixture 3: a mixture of nickel and water
1
The diagrams below represent mixtures 1, 2 and 3.
Match the diagrams to the mixtures.
Write the name of the parts of the mixture under each diagram.
Part 3: Making and separating mixtures
45
2
The four separation methods you have looked at in this lesson are:
sieving, decanting, magnetic attraction and evaporation.
Which separation method would you use to separate these mixtures?
a
the mixture of nickel and sulfur
_________________________________________________________
b
the mixture of copper sulfate and water
_________________________________________________________
c
the mixture of nickel and water
_________________________________________________________
3
The particle model of matter is a useful way of explaining how
evaporation works as a separation method.
Draw a labelled diagram to show how the particles in a mixture of salt
and water can be separated.
46
Mixture separation
Exercise 3.5a: Separating iron filings
1
Complete this sentence.
I separated the iron filings from the mixture by ________________ .
This method is useful for separating substances that are
___________________ from substances that are not.
2
Put the iron filings in a small plastic bag or envelope or wrap them in
paper and seal the parcel with sticky tape.
Then use sticky tape to stick the parcel in the space below.
Part 3: Making and separating mixtures
47
Exercise 3.5b: Separating marble chips
1
Complete this sentence.
I separated the marble chips from the mixture by ________________ .
This method is useful for separating substances which are different
___________________ .
2
Put the marble chips in a small plastic bag or envelope or wrap them in
paper and seal the parcel with sticky tape.
Then use sticky tape to stick the parcel in the space below.
48
Mixture separation
Exercise 3.5c: Separating sand
1
Complete this sentence.
I separated the wet sand from the mixture by______________ . This
method is useful for separating liquids from ______________ .
2
Put the dry sand in a small plastic bag or envelope or wrap them in
paper and seal the parcel with sticky tape.
Then use sticky tape to stick the parcel in the space below.
Part 3: Making and separating mixtures
49
Exercise 3.5d: Separating salt
1
Complete this sentence.
I separated the salt from the water by___________ . This method is
useful for separating a _________ from a liquid.
2
Put the dry salt in a small plastic bag or envelope or wrap them in paper
and seal the parcel with sticky tape.
Then use sticky tape to stick the parcel in the space below.
50
Mixture separation