# A student adds a small amount of bromine water to two test tubes. To the first test tube, the student adds potassium chloride solution. To the second test tube, the student adds potassium iodide solution. Describe what the student would observe in each test tube and explain these observations in terms of displacement reactions.

> AQA A-Level Chemistry (7405) — 3.2.3 Group 7(17), the halogens · Describe and Explain · 5 marks

## Mark scheme (5 marks)

1. No colour change / reaction in the test tube containing potassium chloride solution
2. Bromine cannot displace chloride ions because chlorine is more reactive than bromine / bromine is less reactive than chlorine
3. The test tube containing potassium iodide turns brown / dark brown (or iodine is produced causing a colour change)
4. Bromine displaces iodide ions from potassium iodide solution because bromine is more reactive than iodine
5. A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt / displacement reactions show the relative reactivity of halogens

## Key terms

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

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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-adds-a-small-amount-d5dac5ea) · Published by Druglandscape Ltd.