# Explain why hydrochloric acid is described as a strong acid, and why ethanoic acid is described as a weak acid. Include what is meant by the term 'weak acid' in your answer.

> Eduqas A-Level Chemistry — 3.9 Acid-base equilibria · Explain · 5 marks

> A student has two solutions of equal concentration: one contains hydrochloric acid and the other contains ethanoic acid.

## Mark scheme (5 marks)

1. Hydrochloric acid completely/fully dissociates (ionises) in water
2. Ethanoic acid only partially dissociates (ionises) in water
3. A weak acid is one that partially dissociates / establishes an equilibrium between the dissociated and undissociated forms
4. At equal concentrations, hydrochloric acid produces more hydrogen/H⁺ ions than ethanoic acid
5. Therefore hydrochloric acid has a lower pH than ethanoic acid at the same concentration

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Chemistry](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/explain-why-hydrochloric-acid-is-described-7db0635a) · Published by Druglandscape Ltd.