# Propanoic acid is a carboxylic acid found in some fermented foods. Describe the chemical properties of propanoic acid, including its reactions with metals, carbonates and alkalis. Explain how these reactions show that propanoic acid is a weak acid rather than a strong acid.

> OCR A-Level Chemistry B: Salters (H433) — 6.1 Aromatic compounds, carbonyls and acids · Describe · 5 marks

> Propanoic acid (CH₃CH₂COOH) is a carboxylic acid that belongs to the same homologous series as methanoic acid, ethanoic acid and butanoic acid. Unlike hydrochloric acid, propanoic acid only partially dissociates in water.

## Mark scheme (5 marks)

1. Propanoic acid reacts with metals (e.g. magnesium/zinc) to produce a salt and hydrogen gas
2. Propanoic acid reacts with carbonates to produce a salt, water and carbon dioxide
3. Propanoic acid reacts with alkalis (e.g. sodium hydroxide) to produce a salt and water only (neutralisation)
4. Propanoic acid only partially dissociates / ionises in water, so the concentration of H⁺ ions is lower than for a strong acid of the same concentration
5. Evidence of being a weak acid: higher pH than a strong acid of the same concentration / reacts more slowly with metals or carbonates than a strong acid

## Key terms

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

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/propanoic-acid-is-a-carboxylic-acid-d93e9a7b) · Published by Druglandscape Ltd.