# A geologist finds a mineral sample and dissolves part of it in dilute hydrochloric acid to produce a solution. The geologist carries out qualitative analysis on the solution to identify the ions present. When dilute sodium hydroxide solution is added in excess, a white precipitate forms that dissolves to give a colourless solution. When dilute hydrochloric acid is added to a separate portion of the solution followed by barium chloride solution, a white precipitate forms. Identify the metal ion and the negative ion present in the geologist's solution and describe what each positive result tells the geologist.

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

## Mark scheme (4 marks)

1. The metal ion present is aluminium (Al³⁺)
2. The white precipitate dissolving in excess sodium hydroxide solution shows the metal ion is from an amphoteric/aluminium hydroxide precipitate that redissolves, confirming the ion is Al³⁺ (or Zn²⁺)
3. The negative ion present is sulfate (SO₄²⁻)
4. The white precipitate with barium chloride solution (after acidifying with dilute hydrochloric acid) confirms the presence of sulfate ions

## Key terms

- [qualitative analysis](https://www.gradenine.co.uk/glossary/qualitative-analysis)
- [precipitate](https://www.gradenine.co.uk/glossary/precipitate)
- [sodium hydroxide](https://www.gradenine.co.uk/glossary/sodium-hydroxide)
- [barium chloride](https://www.gradenine.co.uk/glossary/barium-chloride)

## 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-geologist-finds-a-mineral-sample-31dd747b) · Published by Druglandscape Ltd.