Testing Water Purity and Summary of Separation Techniques

This final lesson in the topic brings together everything you have learned about states of matter and separation techniques, as required by the Edexcel GCSE Chemistry specification (1CH0, Topic 1). You will learn how to test for dissolved solids in water, review all separation techniques, and practise choosing the right technique for a given situation. This lesson also covers common exam mistakes and how to write high-quality answers for describe-the-method questions.

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Testing for Dissolved Solids in Water

The Evaporation Test

To determine whether a sample of water contains dissolved solids:

1. Measure a known volume of the water sample (e.g. 50 cm\u00b3) using a measuring cylinder.
2. Weigh a clean, dry evaporating basin and record its mass.
3. Pour the water sample into the evaporating basin.
4. Heat the evaporating basin gently on a tripod and gauze (or water bath) to evaporate all the water.
5. Allow the basin to cool, then re-weigh it.
6. Calculate the mass of the residue: mass of residue = final mass of basin − initial mass of basin.