# A student is investigating the effect of pH on the rate of reaction between sodium thiosulfate solution and hydrogen peroxide solution. They are using a timer to measure the time taken for the reaction to go to completion. Explain the importance of controlling the pH of the hydrogen peroxide solution in this investigation.

> OCR A-Level Chemistry A (H432) — 1.1 Practical skills assessed · Explain · 4 marks

## Mark scheme (4 marks)

1. Understanding the importance of controlling pH in the investigation
2. Relevance of pH to the reaction between sodium thiosulfate and hydrogen peroxide
3. Control of pH in the investigation
4. Explanation of the effect of pH on the rate of reaction

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](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-is-investigating-the-effect-39e2dd4e) · Published by Druglandscape Ltd.