# A student has a sample of rock salt, which contains salt (sodium chloride) dissolved in water along with insoluble mud and grit. The student wants to obtain a pure, dry sample of salt from the mixture. Describe how the student could do this, naming the techniques used at each stage.

> Edexcel GCSE Chemistry (1CH0) — 1.2 Methods of separating and purifying substances · Describe · 4 marks

> Rock salt is a naturally occurring mixture of salt and insoluble rock particles. It can be processed to obtain pure sodium chloride.

## Mark scheme (4 marks)

1. Filter the mixture to remove the insoluble mud and grit (filtration)
2. The salt solution (filtrate) passes through the filter paper and is collected
3. Heat / evaporate the filtrate to remove most of the water
4. Allow the remaining solution to cool so that salt crystals form (crystallisation), then dry the crystals

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