# Aldehydes and ketones are two families of organic compounds that contain the carbonyl group. Explain the difference between an aldehyde and a ketone in terms of the position of the carbonyl group, and describe how Tollens' reagent can be used to distinguish between them, including the observations you would expect for each compound type.

> WJEC A-Level Chemistry (Wales) — 4.4 Aldehydes and ketones · Explain · 5 marks

## Mark scheme (5 marks)

1. In an aldehyde, the carbonyl group (C=O) is at the end of the carbon chain (terminal position) / bonded to at least one hydrogen atom
2. In a ketone, the carbonyl group (C=O) is in the middle of the carbon chain / bonded to two carbon atoms on either side
3. Tollens' reagent is an aqueous solution of silver ions / silver nitrate in ammonia solution (ammoniacal silver nitrate)
4. An aldehyde reduces the silver ions and produces a silver mirror on the inside of the test tube (positive result)
5. A ketone does not react with Tollens' reagent and no silver mirror is formed (negative result) / the solution remains colourless

## Key terms

- [carbonyl group](https://www.gradenine.co.uk/glossary/carbonyl-group)
- [aldehyde](https://www.gradenine.co.uk/glossary/aldehyde)
- [ketone](https://www.gradenine.co.uk/glossary/ketone)
- [Tollens' reagent](https://www.gradenine.co.uk/glossary/tollens-reagent)

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "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/aldehydes-and-ketones-are-two-families-0f2f7d0b) · Published by Druglandscape Ltd.