# When chlorine water is added to a solution of potassium bromide, the solution turns orange-brown. When chlorine water is added to a solution of potassium iodide, the solution turns brown. Explain these observations in terms of displacement reactions and the relative reactivity of the halogens involved.

> Edexcel A-Level Chemistry (9CH0) — 4.2 Group 7 halogens · Explain · 5 marks

> Chlorine, bromine and iodine are halogens in Group 7 of the periodic table. Their reactivity decreases down the group. Displacement reactions between halogens and halide solutions can be used to establish the order of reactivity of the halogens.

## Mark scheme (5 marks)

1. Chlorine displaces bromine from potassium bromide solution
2. Chlorine is more reactive than bromine, so it can displace bromine
3. The orange-brown colour is due to bromine being produced
4. Chlorine displaces iodine from potassium iodide solution
5. Chlorine is more reactive than iodine, so it can displace iodine, which is the brown/dark brown product formed

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/when-chlorine-water-is-added-to-bfa1b23d) · Published by Druglandscape Ltd.