# Butanoic acid is a carboxylic acid responsible for the unpleasant smell of rancid butter. Explain what is meant by the term 'carboxylic acid', and describe what would be observed when butanoic acid solution is added to magnesium ribbon, naming one product formed in this reaction.

> Eduqas A-Level Chemistry — 4.5 Carboxylic acids and their derivatives · Explain · 5 marks

> Butanoic acid has the molecular formula C₃H₇COOH and is a weak acid found in dairy products that have spoiled.

## Mark scheme (5 marks)

1. Carboxylic acids contain the carboxyl / –COOH functional group
2. Carboxylic acids are weak acids (only partially dissociate / ionise in water)
3. Bubbles / fizzing / effervescence observed
4. Magnesium dissolves / disappears (gets smaller / ribbon dissolves)
5. Hydrogen gas is produced (named product)

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/butanoic-acid-is-a-carboxylic-acid-a6ffbc4b) · Published by Druglandscape Ltd.