Separation techniques
In this topic you will:
- use what you know about mixtures to separate them
- choose apparatus to carry out a practical task
- carry out practical work in a safe way.
Key words
- condenser
- conical flask
- filter funnel
- filter paper
Making mixtures
Mixtures contain different substances that are not combined together chemically. You made a mixture with iron filings and sulfur in topic 2.7. You separated the iron and sulfur in your mixture by using a magnet. You used the difference in the properties of iron and sulfur to separate them. Iron is magnetic; sulfur is not magnetic.
Separating mixtures
Copper sulfate and water
The evaporating dish contains a mixture of water and copper sulfate. If it is left in a warm room, the water evaporates and leaves the copper sulfate behind in the dish.
Food dye and water
A mixture of food dye and water can be separated by using a piece of apparatus called a condenser. It is used to separate mixtures of two liquids.
The water and food dye mixture is heated and boils. The liquid water reaches the temperature where it changes state and becomes a gas. Water that is in the gas state is called steam when it has been formed by boiling the water. The gas travels along the tube into the condenser. The cold water that is circulating around the outside of the condenser cools the gas down. This makes the gas condense back into liquid water. The liquid water collects in the beaker. The food dye remains in the heated container.
The food dye and water have different properties that allow you to separate them – they have different boiling points.
Quick Fact
Water boils at 100°C, but food dyes have much higher boiling points. This difference allows them to be separated by distillation.
Questions
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The particles gain energy and escape as steam.
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It is cooled and condenses back into liquid water.
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They have different boiling points. Water boils and becomes a gas first.
Think Like a Scientist
Separating Sandy, Salty Water
Your task is to separate a mixture of sandy and salty water.
You will need: The apparatus shown in the diagrams.
Step 1. Prepare a filter paper and place it in a filter funnel. Place the funnel in the conical flask.
Step 2. Pour the mixture into the funnel. Take care to add it slowly so that the mixture does not go down the outside of the filter paper. Do not disturb the wet filter paper because it tears easily.
Step 3. When you have filtered all the mixture, leave the filter paper in a warm place to dry.
Step 4. Place the clear liquid from the conical flask in an evaporating basin. Wear safety glasses. Heat this gently. When the liquid starts to spit, remove it from the heat.
Step 5. Leave the liquid in a warm place to evaporate.
Questions
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Sand is insoluble in water and too large to pass through the filter paper, so it is separated by filtration.
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Stirring the mixture could tear the wet filter paper, causing solids to pass through and contaminating the filtrate.
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Wear safety goggles, heat the solution gently, and avoid leaning over the evaporating dish as it may spit.
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You would need to use distillation to collect the water vapor, condense it, and recover it as liquid water.
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You could filter the solution again before evaporation, or redissolve the salt in clean water and filter it to remove impurities.
Think Like a Scientist
Separating Two Solids
If you mix powdered black carbon and table salt together you have a mixture of two solids.
How can you separate the carbon from the salt?
What do you know about the properties of carbon powder and table salt that might be useful here?
Make a plan of how you could do this. Remember to think about safety.
Make a list of the equipment you would need.
Discuss it in your group.
Share your ideas with the class.
Did you change any of your ideas when you discussed them with the class?
Carry out your plan, once it has been checked for safety.
Questions
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Carbon is insoluble in water, while salt dissolves easily. This difference allows separation by dissolving and filtering.
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Beaker, stirring rod, water, filter paper, funnel, evaporating dish, heat source, tongs, goggles.
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Add water to the mixture, stir to dissolve the salt, and filter to remove carbon. Evaporate the filtrate to recover the salt.
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Wear goggles when heating, handle glassware carefully, and avoid inhaling fine powders like carbon dust.