# Citric acid is a weak acid found in citrus fruits. Hydrochloric acid is a strong acid. Both acids can be prepared as solutions with the same concentration. Explain why a solution of citric acid at a given concentration has a higher pH than a solution of hydrochloric acid at the same concentration.

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

> Citric acid (H₃C₆H₅O₇) is a weak acid naturally present in lemons and other citrus fruits. Hydrochloric acid (HCl) is a strong acid commonly used in industry and laboratories.

## Mark scheme (5 marks)

1. Hydrochloric acid is fully/completely ionised (dissociated) in aqueous solution
2. Citric acid is only partially ionised (dissociated) in aqueous solution
3. Therefore the concentration of hydrogen ions (H⁺) is lower in the citric acid solution than in the hydrochloric acid solution at the same concentration
4. pH is a measure of hydrogen ion concentration / higher [H⁺] gives lower pH
5. Because citric acid has a lower [H⁺] than HCl at the same concentration, citric acid has a higher pH

## 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/citric-acid-is-a-weak-acid-c4a605a0) · Published by Druglandscape Ltd.