# A student has two unlabelled test tubes. One contains an alkane and the other contains an alkene. Describe how the student could use bromine water to identify which test tube contains the alkene. Include the observations expected for both test tubes.

> AQA A-Level Chemistry (7405) — 3.3.6 Organic analysis · Describe · 5 marks

## Mark scheme (5 marks)

1. Add bromine water to each test tube / add bromine water to both samples
2. The alkene decolourises / turns the bromine water from orange to colourless
3. The alkane does not decolourise the bromine water / bromine water stays orange with the alkane
4. The alkene reacts with bromine water because it is unsaturated / has a carbon–carbon double bond
5. The alkane does not react with bromine water because it is saturated / has no double bond

## 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 AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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-has-two-unlabelled-test-5952bc05) · Published by Druglandscape Ltd.