# Propanoic acid is a carboxylic acid used as a food preservative. Explain why propanoic acid is described as a weak acid, and state two observable changes that occur when propanoic acid reacts with magnesium.

> Cambridge International IGCSE Chemistry (0620) — 11.7 Carboxylic acids · Explain · 4 marks

> Propanoic acid, CH₃CH₂COOH, is a carboxylic acid that can react with metals such as magnesium.

## Mark scheme (4 marks)

1. Propanoic acid is partially / incompletely ionised (dissociated) in aqueous solution
2. It produces a lower concentration of H⁺ ions than a strong acid of the same concentration
3. Bubbles / effervescence are produced (hydrogen gas is given off)
4. The magnesium dissolves / disappears

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/propanoic-acid-is-a-carboxylic-acid-05a51276) · Published by Druglandscape Ltd.