# Alkanes and alkenes are two families of hydrocarbons. Describe how bromine water can be used to distinguish between an alkane and an alkene, and explain why each hydrocarbon produces the result it does.

> WJEC A-Level Chemistry (Wales) — 2.5 Hydrocarbons · Describe and Explain · 5 marks

## Mark scheme (5 marks)

1. Bromine water remains orange/brown (unchanged) with the alkane
2. Bromine water is decolourised / turns colourless with the alkene
3. Alkanes are saturated / contain only single C–C bonds, so they cannot react with bromine water
4. Alkenes are unsaturated / contain a carbon–carbon double bond
5. The alkene reacts with bromine water by addition across the double bond, breaking it and removing the bromine from solution

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](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/alkanes-and-alkenes-are-two-families-05dc3107) · Published by Druglandscape Ltd.