# A student carries out qualitative analysis on an unknown solution. When a few drops of sodium hydroxide solution are added, a green precipitate forms. When dilute hydrochloric acid followed by barium chloride solution is added to a fresh sample of the unknown solution, a white precipitate forms. Identify the cation and the anion present in the unknown solution, and describe what these observations show.

> Edexcel GCSE Chemistry (1CH0) — 9.1 Qualitative analysis: tests for ions (Chem only) · Describe · 4 marks

> A student is given an unknown solution and is asked to identify the ions it contains using qualitative analysis tests.

## Mark scheme (4 marks)

1. The cation is Fe²⁺ (iron(II) ions)
2. The green precipitate is iron(II) hydroxide, formed when OH⁻ ions react with Fe²⁺ ions
3. The anion is SO₄²⁻ (sulfate ions)
4. The white precipitate with barium chloride solution confirms the presence of sulfate ions (barium sulfate is formed)

## Key terms

- [qualitative analysis](https://www.gradenine.co.uk/glossary/qualitative-analysis)
- [precipitate](https://www.gradenine.co.uk/glossary/precipitate)
- [cation](https://www.gradenine.co.uk/glossary/cation)
- [anion](https://www.gradenine.co.uk/glossary/anion)

## Related

- [Revision notes for Edexcel GCSE Chemistry (1CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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-carries-out-qualitative-analysis-741220a2) · Published by Druglandscape Ltd.