# A student is preparing a sample of copper sulfate crystals in a school laboratory. They dissolve excess copper oxide in dilute sulfuric acid, then use an appropriate separation technique to obtain dry copper sulfate crystals from the resulting solution. Explain why crystallisation is the most appropriate separation technique to use in this situation, and describe how the student would carry out crystallisation to obtain dry copper sulfate crystals.

> OCR A-Level Chemistry B: Salters (H433) — 2.2 Amount of substance · Explain · 5 marks

> Copper sulfate is a soluble solid that can be obtained from its solution by removing the water solvent in a controlled way.

## Mark scheme (5 marks)

1. Crystallisation is appropriate because copper sulfate is a soluble solid (that needs to be separated from its solution / the water solvent)
2. The solution is heated (in an evaporating dish) until crystals start to form
3. Leave the solution to cool (slowly) so that more crystals form
4. Filter the crystals from the remaining solution
5. Pat dry / leave to dry at room temperature (or in a low-temperature oven) to obtain dry crystals

## Key terms

- [crystallisation](https://www.gradenine.co.uk/glossary/crystallisation)

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-is-preparing-a-sample-e6815676) · Published by Druglandscape Ltd.