# A student has prepared a sample of copper(II) sulfate crystals that are contaminated with a small amount of an insoluble black solid. Describe how the student could obtain a pure, dry sample of copper(II) sulfate crystals from this contaminated mixture.

> Cambridge International IGCSE Chemistry (0620) — 12.4 Separation and purification · Describe · 4 marks

## Mark scheme (4 marks)

1. Dissolve the contaminated copper(II) sulfate in hot water to make a solution
2. Filter the solution to remove the insoluble black solid (residue), collecting the filtrate
3. Heat / evaporate the filtrate until the point of crystallisation (until saturated), then allow to cool
4. Filter off the crystals and pat/dry them (e.g. between filter paper or leave to dry in a warm oven)

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