How can mixtures be separated into different materials?
Mixtures of materials
What is a mixture? A mixture is two or more different materials that have been mixed together.
In some mixtures, the different materials are still clearly visible after mixing. A mixture of peanuts and raisins would be an example of such a mixture. How would we separate the peanuts and the raisins? Well, we could simply pick the raisins out of the peanuts!
A mixture of peanuts and raisins
Can you think of other mixtures in which the different materials are still clearly visible after mixing? Look at the pictures below for some ideas.
A mixture of different coloured jelly beansA mixture of different fruits in a fruit saladA mixture of swans and ducks on a lakeA mixture of red, green, yellow and orange sweet peppersA mixture of pink, yellow and white flowersA mixture of different shells from the beach
In other mixtures, the materials are mixed so thoroughly that it seems one material has 'disappeared' into the other. Such mixtures are called solutions. We will learn more about solutions shortly.
Making mixtures
First, we will have some fun making mixtures.
Mixing solids
MATERIALS:
500g bag of barley (beans or lentils will also do)
500g bag of rice
Small packet of sugar
Clean sand (from the beach or from a building site)
Plastic spoons for scooping
Small yoghurt tubs or paper cups for mixing
Sieve (the type used for sieving flour)
You need a sieve (or strainer) that is coarse enough to let all the sugar through. A suggestion is to sieve the sugar first. Whatever passes through the sieve can be used in class.
INSTRUCTIONS (Part 1):
Place 10 scoops of barley in the mixing tub.
Place 10 scoops of rice in the mixing tub.
Stir the barley and rice until they are mixed.
Answer the questions below.
QUESTIONS:
Can you still see the individual rice and barley grains?
Yes.
Draw a picture of the mixture.
Separate the mixture into a pile of rice grains and a pile of barley grains. Write a sentence to explain how you separated the mixture.
The learners may answer: 'I picked the barley grains out of the rice' or 'I picked the rice grains out of the barley'.
Did the barley and rice grains change in any way, or do they still look the same as before they were mixed?
The grains still look the same.
INSTRUCTIONS (Part 2):
Place 10 scoops of rice in the mixing tub.
Place 10 scoops of sugar in the mixing tub.
Stir the sugar and rice until they are mixed.
Answer the questions below.
QUESTIONS:
Can you still see the individual rice and sugar grains?
Yes.
Draw a picture of the mixture.
Separate the mixture into a pile of rice grains and a pile of sugar grains. Write a sentence to explain how you separated the mixture.
The learners may answer: 'I picked the rice grains out of the sugar'.
Can you think of a quick way to separate the mixture, using a sieve? Describe what you would do to separate the mixture. Describe what would happen to the mixture.
I would put the mixture in the sieve. The sugar grains will fall through the sieve and the rice grains will stay behind.
Did the sugar and rice grains change in any way, or do they still look the same as before they were mixed?
The grains still look the same.
INSTRUCTIONS (Part 3):
Teacher note: This part of the activity needs to be planned-for by the teacher. The sand and sugar must be of the same average grain size and should be sieved in advance to ensure this is so. The impact of the uselessness of sieving will be partially or totally lost otherwise.
Place 10 scoops of sand in the mixing tub.
Place 10 scoops of sugar in the mixing tub.
Stir the sugar and sand until they are mixed.
Answer the questions below.
QUESTIONS:
Draw a picture of the mixture.
Can you separate the mixture into a pile of sand grains and a pile of sugar grains? How long would it take if you picked the sand grains out of the sugar one by one?
The learners may answer: 'It would be possible but it would take a very long time.'
Do you think that it would be possible to separate the mixture using a sieve? Why do you think so?
It would not be possible to separate the mixture with the sieve, because the sugar grains and the sand grains are both small enough to fall through the sieve.
In the previous activity we mixed solid materials with different sized grains and learnt that:
when the grains are large enough, we can separate them by hand; and
when the two materials have grains of different sizes they can be separated by sieving.
In the next activity we will explore mixtures of solids and liquids.
Mixing a solid and a liquid
MATERIALS:
clean sand (from the beach or from a building site)
plastic spoons for scooping
small yoghurt tubs or paper cups for mixing
sieve (the type used for sieving flour)
kitchen towel or paper towel
INSTRUCTIONS:
Place 5 scoops of sand in the mixing tub.
Pour water into the mixing tub until it is half-full.
Stir the sand and water until they are mixed.
Answer the questions below.
QUESTIONS:
Can you still see the individual sand grains?
Yes.
Draw a picture of the mixture.
Can you separate the mixture into a pile of sand grains and water?. How long would it take if you picked the sand grains out of the water one by one?
The learners may answer: 'It would be possible but it would take a very long time'.
Would it be possible to separate the sand from the water using the sieve? Say why or why not.
No, it would not be possible, because the grains and the water would both pass through the sieve.
Would it be possible to separate the sand from the water using the paper towel? If you think it would be possible, explain what you would do.
Yes, it would be possible. I would pour the mixture through the towel. The sand will stay behind on the towel, while the water will pass through it.
Do you think it would be possible to separate sugar and water in the same way (by filtering the mixture through a towel)? Say why or why not.
I think it would not be possible because the sugar will dissolve in the water and also pass through the towel.
In the previous activity we mixed a solid material (sand) with a liquid (water) and learnt that sometimes a mixture of liquid and solid can be separated by filtering. In the activity the towel was used as a filter.
Is it possible to mix liquids? Can you think of examples of mixtures of liquids? Look at the picture below for some ideas.
That is right Tom. Let's look at some liquids which are not so easy to mix together.
Mixing liquids
MATERIALS:
water
cooking oil
plastic spoons for scooping
small glass or transparent plastic cup for mixing
INSTRUCTIONS:
Place 10 scoops of water in the mixing tub.
Place 10 scoops of cooking oil in the mixing tub.
Stir the oil and water until they are mixed.
Let the mixture stand for a few minutes, then answer the questions below.
QUESTIONS:
Did the liquids mix? Describe what the mixture looks like.
The two liquids did not mix. There are two liquid layers.
Draw a picture of the mixture.
Do you think it would be possible to scoop all the oil out of the water? How long do you think it would take?
The learners may answer: 'It would be possible to scoop out some of the oil but it would take a very long time. I don't think it would be possible to get all the oil out of the water'.
Would it be possible to separate the liquids using a sieve or a filter? Say why or why not.
No, it would not be possible, because the oil and the water would both pass through the sieve and the filter.
Can you think of another way to separate the mixture into oil and water? If you think it would be possible, explain what you would do.
Learners may suggest pouring (decanting) the oil from the water.
Do you think it would be possible to separate a mixture of juice and water using any of the methods that we have used so far (hand-separating, sieving, filtering or decanting)? Say why or why not.
I don't think it will be possible because the juice and water will be mixed too thoroughly.
The real reason is that the juice will be dissolved in the water, which means the substances are mixed on a level of individual particles, but learners may not be able to put this into words yet.
In the previous activity we mixed two liquids (water and oil) and learned that sometimes a mixture of two liquids can be separated by decanting.
Separating mixtures
In the next section we will summarise all the different ways of separating mixtures. We have made different mixtures and tried to separate them using a variety of methods. In this section we will revise all these separation methods.
Separating mixtures
INSTRUCTIONS (Part 1)
The table below contains pictures of mixtures.
For each of the mixtures in the table, write which materials it is made up of in the middle column.
Write how you would separate the mixture in the column on the right.
Picture of mixture
Materials in the mixture
How the mixture could be separated
Peanuts and raisins
Pick the raisins out of the mixture. The peanuts will remain.
Spaghetti and meatballs
Pick the spaghetti out of the sauce, which will remain behind.
Peach, plum, banana and berries
Pick out the berries, followed by the banana pieces, etc. until all the ingredients have been separated.
Boys and girls
Tell the boys to stand on one side of the class and the girls to stand on the other side.
INSTRUCTIONS (Part 2)
The table below contains descriptions of mixtures.
For each of the mixtures in the table, write which states it is made of in the middle column (solid, liquid or gas).
Write how you would separate the mixture in the column on the right.
Description of mixture
States in the mixture
How the mixture could be separated
Water and oil
Liquid and liquid
Decant the oil off the top.
Water and sand
Liquid and solid
Decant the water off the sand, or filter the mixture.
Sugar and rice
Solid and solid
Pick the rice out of the sugar, or sieve the mixture through a sieve with holes that are small enough to let the sugar through but not the rice grains.
It is possible to mix materials in many different combinations. In a mixture, the materials that have been mixed do not change. They keep their individual properties. Sometimes it is possible to separate a mixture into the individual materials again.
Amixture consists of two or more different materials mixed together.
Sometimes mixtures can be separated into the individual materials again.
Some of the ways in which mixtures can be separated are: sieving, filtering, hand sorting, and settling followed by decanting.
When a material changes from a solid to a liquid, the process is called melting.
When a material forms a solution in another material, the process is called dissolving.
Melting and dissolving are two different processes.
What is a mixture?
A mixture is made when we mix two or more materials together.
List six different ways in which solids, liquids and gases can be combined to form mixtures.
Combine a solid with a solid.
Combine a solid with a liquid.
Combine a solid with a gas.
Combine a liquid with a liquid.
Combine a liquid with a gas.
Combine a gas with a gas.
Did you know that the air we breathe is actually a mixture of many gases? The pie chart below shows all the different gases in clean air.
Use the information in the pie chart and make a list of all the gases that are found in clean air.
Which gas is the most abundant in air? (Which gas is found in the largest amount?) What percentage of this gas is present in clean air?
What percentage of oxygen is present in air?
If you had 5000 air particles, how many of these particles would be oxygen particles?
Nitrogen, oxygen, argon, carbon dioxide, and other gases.
Nitrogen, 78%.
20.9%
20.9% of 5000 particles are oxygen particles.
Therefore, no of oxygen particles = 20.9 % of 5000
