# A student dissolves an unknown white solid in water. The solution is tested with Universal Indicator and a pH of 2 is recorded. The student then adds a spatula of sodium hydroxide powder to the solution and stirs. Explain what happens to the pH of the solution as the sodium hydroxide is added, and state the type of reaction occurring.

> WJEC GCSE Chemistry (Wales) — 2.2 Acids, bases and salts · Explain · 4 marks

> Sodium hydroxide is a base. A solution with a pH of 2 is strongly acidic.

## Mark scheme (4 marks)

1. The pH increases (as sodium hydroxide is added)
2. Because the sodium hydroxide neutralises the acid / the alkali reacts with the acid
3. If enough sodium hydroxide is added the pH will reach 7 (neutral) / the pH could rise above 7 if excess sodium hydroxide is added
4. The type of reaction is neutralisation

## Key terms

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

## Related

- [Revision notes for WJEC GCSE Chemistry (Wales)](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/a-student-dissolves-an-unknown-white-8489a86e) · Published by Druglandscape Ltd.