# Describe how a pure, dry sample of sodium chloride could be prepared by reacting sodium hydroxide solution with dilute hydrochloric acid. Include in your answer how you would determine the exact volume of acid required.

> Cambridge International IGCSE Chemistry (0620) — 7.3 Preparation of salts · Describe · 4 marks

## Mark scheme (4 marks)

1. Use an indicator (e.g. litmus) to find the exact volume of acid needed to neutralise the sodium hydroxide
2. Repeat the procedure using the same volumes but without the indicator
3. Evaporate / heat the solution to concentrate it (until a small volume / saturated solution remains)
4. Leave to cool / crystallise, then filter and dry the crystals (e.g. between filter paper / in a warm oven)

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