# A student adds a few drops of sodium hydroxide solution to four separate test tubes, each containing a solution of a different metal salt. Describe what the student would observe in each test tube if the solutions contained iron(II) ions, iron(III) ions, copper(II) ions, and calcium ions respectively, and explain what these observations indicate about transition metals and calcium.

> OCR GCSE Chemistry A: Gateway Science (J248) — C4.2 Identifying the products of chemical reactions · Describe · 4 marks

> Sodium hydroxide solution is commonly used as a reagent to identify cations in solution. Different metal ions produce characteristic precipitates when sodium hydroxide solution is added.

## Mark scheme (4 marks)

1. Iron(II) ions produce a green precipitate with sodium hydroxide solution
2. Iron(III) ions produce an orange/brown precipitate with sodium hydroxide solution
3. Copper(II) ions produce a blue precipitate with sodium hydroxide solution
4. Calcium ions produce a white precipitate with sodium hydroxide solution; the coloured precipitates from iron(II), iron(III), and copper(II) show that transition metals form coloured compounds, whereas calcium (which is not a transition metal) forms a white precipitate

## Key terms

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

## Related

- [Revision notes for OCR GCSE Chemistry A: Gateway Science (J248)](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-adds-a-few-drops-c4f5f236) · Published by Druglandscape Ltd.