# A student heats a sample of an unknown metal compound on a nichrome wire loop in a flame and observes a lilac colour. The student then adds dilute nitric acid followed by silver nitrate solution to a solution of the same compound and observes a pale yellow precipitate. Explain what these two observations tell the student about the identity of the compound.

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

> Flame tests and precipitation reactions are qualitative tests used to identify the ions present in an unknown compound.

## Mark scheme (4 marks)

1. The lilac flame colour identifies the presence of potassium ions (cations)
2. The flame test is a qualitative test used to identify metal ions (cations)
3. The pale yellow precipitate with silver nitrate solution identifies bromide ions (halide ions / Br⁻)
4. Therefore the compound is potassium bromide

## Key terms

- [precipitate](https://www.gradenine.co.uk/glossary/precipitate)

## Related

- [Revision notes for OCR GCSE Chemistry A: Gateway Science (J248)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" 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-heats-a-sample-of-d426399f) · Published by Druglandscape Ltd.