# Chlorine gas is bubbled through potassium bromide solution. The colourless solution turns orange-brown. Explain this colour change in terms of oxidation and reduction, identifying which species is oxidised and which is reduced. Give the ionic equation for the reaction.

> AQA A-Level Chemistry (7405) — 3.1.7 Oxidation, reduction and redox equations · Explain · 5 marks

> Chlorine is a more reactive halogen than bromine. When chlorine is bubbled through potassium bromide solution, a displacement reaction occurs and the solution turns orange-brown.

## Mark scheme (5 marks)

1. Bromide ions are oxidised (lose electrons)
2. Chlorine molecules are reduced (gain electrons)
3. Bromine molecules (Br₂) are formed and are responsible for the orange-brown colour
4. Correct ionic equation: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂
5. The reaction is described as redox because oxidation and reduction occur simultaneously

## Key terms

- [oxidation](https://www.gradenine.co.uk/glossary/oxidation)
- [reduction](https://www.gradenine.co.uk/glossary/reduction)
- [ionic equation](https://www.gradenine.co.uk/glossary/ionic-equation)

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- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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