# A chemist has three unlabelled bottles. Each bottle contains one of the following liquids: an alkane, an alkene, or a carboxylic acid. Describe how the chemist could use two different chemical tests to identify which bottle contains the alkene and which bottle contains the carboxylic acid. State the expected observations for each test.

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

## Mark scheme (5 marks)

1. Add bromine water to each sample
2. The alkene decolourises / turns the bromine water from orange to colourless
3. The alkane and carboxylic acid do not decolourise bromine water (no change / remains orange)
4. Add sodium carbonate (or sodium hydrogencarbonate) to the remaining two samples to identify the carboxylic acid
5. The carboxylic acid produces bubbles / effervescence (carbon dioxide gas is produced) with sodium carbonate; the alkane shows no reaction

## Key terms

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

## 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-chemist-has-three-unlabelled-bottles-28a3b1f8) · Published by Druglandscape Ltd.