Separating mixtures Cambridge IGCSE Co-ordinated Sciences (Double Award) revision
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In plain words
To separate a mixture, find a way the parts differ and use it. One dissolves and the other doesn't? Filter. A solid dissolved in a liquid? Evaporate the liquid off, or distil it if you want to keep the liquid. Two liquids with different boiling points? Fractional distillation.
Three things to know
- Filtration separates an insoluble solid from a liquid. Crystallisation (evaporation) gets a dissolved solid out of a solution.
- Simple distillation gets the solvent out of a solution, such as pure water from salt water. Fractional distillation separates liquids with different boiling points.
- The solid left on the filter paper is the residue. The liquid that runs through is the filtrate.
Tips and tricks
- Match the method to the difference: filtration (one is insoluble), crystallisation (a dissolved solid), distillation (different boiling points), chromatography (different solubilities in a solvent).
- To get dry crystals, don't boil the solution dry. Heat until crystals start to form, leave it to cool, then filter and dry them.
It lands in your notebook with its questions as flashcards.
Separating mixtures: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which method separates an insoluble solid from a liquid?
The solid is caught by the filter paper.
Which method gets salt crystals from salt solution?
Evaporating the water leaves the salt behind.
In filtration, what is the solid left on the filter paper called?
The filtrate is the liquid that passes through.
Fractional distillation separates liquids that have different what?
The liquid with the lower boiling point boils off first.
Which piece of apparatus turns the vapour back into a liquid in distillation?
Cold water around the condenser cools the vapour.
Which is the best method to separate two liquids that mix completely?
It relies on their different boiling points.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
4 questions, 8 marks. Write your answers on paper, then check them.
Separating mixtures
Cambridge IGCSE Co-ordinated Sciences (Double Award) 0654 · 8 marks · papermunch.org
Name ______________________________ Date ______________
Describe how to get pure, dry sand and salt crystals from a mixture of sand and salt.[3]
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Add water and stir to dissolve the salt. Filter: the sand stays on the paper (wash and dry it). Evaporate the filtrate to leave salt crystals.
Name the method used to get pure water from sea water, and explain why it works.[2]
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Simple distillation. The water boils off and is condensed back to a liquid; the salt is left behind.
Explain why a mixture of ethanol and water can be separated by fractional distillation.[2]
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They have different boiling points (ethanol 78 °C, water 100 °C), so the ethanol boils off first.
State the name given to the liquid that passes through filter paper.[1]
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The filtrate.
Answers: Separating mixtures
- 1. Add water and stir to dissolve the salt. Filter: the sand stays on the paper (wash and dry it). Evaporate the filtrate to leave salt crystals.
- 2. Simple distillation. The water boils off and is condensed back to a liquid; the salt is left behind.
- 3. They have different boiling points (ethanol 78 °C, water 100 °C), so the ethanol boils off first.
- 4. The filtrate.