# Hydrochloric acid and ethanoic acid are both acids used in laboratories. Explain why hydrochloric acid is described as a strong acid and ethanoic acid is described as a weak acid, and explain how this difference affects the pH of two solutions that have the same concentration.

> Edexcel A-Level Chemistry (9CH0) — 12.1 Strong and weak acids · Explain · 5 marks

> Hydrochloric acid has a concentration of 0.1 mol/dm³. Ethanoic acid also has a concentration of 0.1 mol³.

## Mark scheme (5 marks)

1. Hydrochloric acid completely/fully dissociates (ionises) in water
2. Ethanoic acid only partially/incompletely dissociates (ionises) in water
3. Hydrochloric acid produces a higher concentration of hydrogen ions (H⁺) than ethanoic acid at the same concentration
4. Hydrochloric acid therefore has a lower pH than ethanoic acid (at the same concentration)
5. pH decreases as hydrogen ion concentration increases (linking lower pH to greater H⁺ concentration)

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](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/hydrochloric-acid-and-ethanoic-acid-are-95018247) · Published by Druglandscape Ltd.