# Butanoic acid is responsible for the distinctive smell of rancid butter. Explain the chemical nature of butanoic acid, including its functional group, its position within a homologous series, and how its acidic properties are typically demonstrated in a reaction with sodium carbonate.

> OCR A-Level Chemistry A (H432) — 6.1 Aromatic compounds, carbonyls and acids · Explain · 5 marks

> Butanoic acid is a carboxylic acid found in rancid butter. It has a pungent, unpleasant odour and is soluble in water.

## Mark scheme (5 marks)

1. Butanoic acid contains the functional group –COOH
2. Butanoic acid is a member of the carboxylic acids homologous series
3. Butanoic acid reacts with sodium carbonate to produce carbon dioxide gas (effervescence / bubbles)
4. A salt and water are also produced in the reaction with sodium carbonate
5. This reaction demonstrates the typical acidic properties of carboxylic acids / carboxylic acids react with carbonates in the same way as other acids

## Key terms

- [functional group](https://www.gradenine.co.uk/glossary/functional-group)
- [homologous series](https://www.gradenine.co.uk/glossary/homologous-series)
- [sodium carbonate](https://www.gradenine.co.uk/glossary/sodium-carbonate)

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](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/butanoic-acid-is-responsible-for-the-92a1282b) · Published by Druglandscape Ltd.