# Ethene undergoes an addition reaction with bromine water. Describe what is observed when ethene is bubbled through bromine water, and explain why ethene reacts in this way whilst ethane does not.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 4.4 Alkenes · Describe and Explain · 4 marks

## Mark scheme (4 marks)

1. Bromine water is decolourised (turns from orange/brown to colourless)
2. Ethene is unsaturated / contains a carbon–carbon double bond
3. The double bond opens / breaks, allowing bromine to add across it (addition reaction)
4. Ethane is saturated / has only single bonds, so it cannot undergo an addition reaction with bromine

## Key terms

- [addition reaction](https://www.gradenine.co.uk/glossary/addition-reaction)
- [bromine water](https://www.gradenine.co.uk/glossary/bromine-water)

## Related

- [Revision notes for Pearson Edexcel International GCSE Chemistry (4CH1)](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/ethene-undergoes-an-addition-reaction-with-2f3694c8) · Published by Druglandscape Ltd.