# A student is given three unlabelled bottles, each containing a different colourless liquid: chloroethane (a haloalkane), ethanol (an alcohol), and water. Describe how the student could use chemical tests to identify which bottle contains the haloalkane and which contains the alcohol. Include the expected observations for each test.

> OCR A-Level Chemistry B: Salters (H433) — 4.2 Alcohols, haloalkanes and analysis · Describe · 5 marks

> Haloalkanes contain a halogen atom bonded to a carbon chain. Alcohols contain an –OH group. Both groups of compounds have distinct chemical properties that can be used to tell them apart from each other and from water.

## Mark scheme (5 marks)

1. Add silver nitrate solution (after hydrolysis with sodium hydroxide/warm with water) OR add sodium metal to identify the alcohol — alcohol reacts with sodium to produce bubbles of hydrogen gas
2. To test for the haloalkane: warm the liquid with sodium hydroxide solution to hydrolyse the C–halogen bond, releasing halide ions into solution
3. Acidify the resulting solution with dilute nitric acid, then add silver nitrate solution
4. A white/cream precipitate forms with the haloalkane sample, confirming the presence of halide ions (chloride ions give a white precipitate with silver nitrate)
5. Water produces no reaction / no precipitate with silver nitrate and no bubbles with sodium, so the bottle that gives neither positive result is identified as water

## Key terms

- [haloalkane](https://www.gradenine.co.uk/glossary/haloalkane)
- [alcohol](https://www.gradenine.co.uk/glossary/alcohol)

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](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-is-given-three-unlabelled-b3e5da9c) · Published by Druglandscape Ltd.