# A student adds a few drops of dilute sodium hydroxide solution to separate aqueous solutions of iron(II) sulfate and iron(III) sulfate. Describe what the student would observe in each test, and explain what these observations show about the ions present.

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

> Iron(II) ions and iron(III) ions both react with hydroxide ions to form precipitates. These reactions can be used to identify transition metal ions in aqueous solution.

## Mark scheme (5 marks)

1. Iron(II) sulfate produces a green precipitate
2. The green precipitate is iron(II) hydroxide / Fe(OH)₂
3. Iron(III) sulfate produces a red-brown precipitate
4. The red-brown precipitate is iron(III) hydroxide / Fe(OH)₃
5. The two precipitates have different colours, so sodium hydroxide solution can be used to distinguish between iron(II) ions and iron(III) ions

## Key terms

- [sodium hydroxide solution](https://www.gradenine.co.uk/glossary/sodium-hydroxide-solution)
- [aqueous solution](https://www.gradenine.co.uk/glossary/aqueous-solution)

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-adds-a-few-drops-bdf25094) · Published by Druglandscape Ltd.