# A student carries out tests on four unlabelled aqueous solutions, each containing a different metal ion. The solutions contain copper(II) ions, iron(III) ions, calcium ions, and zinc ions respectively. Describe how the student could use aqueous sodium hydroxide solution to identify which solution contains copper(II) ions, which contains iron(III) ions, and which contains zinc ions. Include the observations the student would make for each ion.

> AQA A-Level Chemistry (7405) — 3.2.6 Reactions of ions in aqueous solution (A-Level only) · Describe · 5 marks

> Aqueous sodium hydroxide can be used to identify metal ions in solution by the colour of the precipitate formed.

## Mark scheme (5 marks)

1. Adding aqueous sodium hydroxide to the copper(II) ion solution produces a blue precipitate
2. Adding aqueous sodium hydroxide to the iron(III) ion solution produces a brown/rust-coloured precipitate
3. Adding aqueous sodium hydroxide to the zinc ion solution produces a white precipitate
4. The white precipitate from the zinc ion solution dissolves when excess sodium hydroxide is added
5. The calcium ion solution also produces a white precipitate with sodium hydroxide, but this precipitate does NOT dissolve in excess sodium hydroxide, allowing calcium to be distinguished from zinc

## Key terms

- [aqueous sodium hydroxide](https://www.gradenine.co.uk/glossary/aqueous-sodium-hydroxide)
- [copper(II) ions](https://www.gradenine.co.uk/glossary/copper-ii-ions)
- [iron(III) ions](https://www.gradenine.co.uk/glossary/iron-iii-ions)
- [zinc ions](https://www.gradenine.co.uk/glossary/zinc-ions)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-carries-out-tests-on-5dc40b82) · Published by Druglandscape Ltd.