Distillation (AQA GCSE Chemistry): Revision Notes
📚 Revision Notes
Distillation
What is distillation?
Distillation is a way to separate a liquid from a mixture. It works by heating the mixture and then cooling the vapour back into liquid. This method uses the different boiling points of substances to separate them.
Types of distillation
There are two main types of distillation you need to know about:
Simple distillation
Simple distillation separates one liquid from a mixture. You can use it to:
- Get pure water from salt water
- Separate ethanol from water
How it works:
- Heat the mixture in a flask
- The liquid with the lower boiling point turns to vapour first
- The vapour travels through a condenser
- Cold water cools the vapour back into liquid (called the distillate)
- The distillate is collected in a separate container
Fractional distillation
Fractional distillation separates mixtures that contain more than two liquids. It uses a special column packed with glass beads.
How it works:
- The mixture is heated in a flask
- Vapours rise up through the fractionating column
- The glass beads help separate the different liquids
- Liquids with different boiling points leave the column at different times
- The liquid with the lowest boiling point comes out first
- Each liquid is collected separately
How the condenser works
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The condenser is a key part of distillation equipment:
- It has two tubes, one inside the other
- Cold water flows between the two tubes
- This keeps the condenser cold
- The cold surface turns vapour back into liquid
- The cooling water never mixes with the substance being separated
Important safety points
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When distilling ethanol and water:
- Never use a Bunsen burner - ethanol is flammable
- Always use an electrical heater instead
- This prevents fires and explosions
Key facts to remember
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Key Points to Remember:
- Ethanol boils at - this is lower than water's boiling point ()
- The substance with the lower boiling point always comes out first
- In fractional distillation, liquids come out in order of increasing boiling point
- The condenser must stay cold to work properly
Example
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Worked Example: Distilling Ethanol and Water
If you distil a mixture of ethanol and water:
- Heat the mixture using an electrical heater (safety first!)
- Ethanol boils first because it has the lower boiling point
- Ethanol vapour travels to the condenser
- Cold water cools the ethanol vapour back to liquid
- Pure ethanol is collected as the distillate
Remember!
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Essential Takeaways:
- Distillation separates liquids using their different boiling points
- Simple distillation is for mixtures with one main liquid to separate
- Fractional distillation is for mixtures with several different liquids
- The condenser uses cold water to turn vapour back into liquid
- Always use electrical heating with flammable substances like ethanol
- The substance with the lowest boiling point always comes out first