# A student is given four unlabelled liquids. The liquids are ethanol, ethanoic acid, propene and octane. The student uses two chemical tests to identify each liquid. Describe the two tests, the observations for each liquid, and explain why each observation occurs.

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

> The student has access to bromine water and sodium carbonate solution.

## Mark scheme (5 marks)

1. Bromine water decolourises / turns from orange to colourless with propene (alkene)
2. Bromine water remains orange with ethanol, ethanoic acid and octane (no reaction / not decolourised)
3. Propene decolourises bromine water because it is unsaturated / has a carbon–carbon double bond that reacts with bromine
4. Sodium carbonate solution produces bubbles / effervescence with ethanoic acid (carboxylic acid reacts with carbonate to produce carbon dioxide)
5. Ethanol and octane show no reaction / no bubbles with sodium carbonate solution, allowing ethanoic acid to be distinguished from the remaining two liquids

## 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)
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