# A student is investigating the rate of a reaction between marble chips and hydrochloric acid by collecting the gas produced using a gas syringe. Explain how the student should carry out a fair and reliable investigation, including how they would record and process their results.

> OCR A-Level Chemistry A (H432) — 1.1 Practical skills assessed · Explain · 5 marks

> Marble chips react with hydrochloric acid to produce carbon dioxide gas. A student plans to compare the volume of gas collected over time at two different concentrations of hydrochloric acid.

## Mark scheme (5 marks)

1. Identify and control a named variable (e.g. mass/size of marble chips, volume of acid, temperature) to make it a fair test
2. Read the gas syringe / volume of gas at regular, stated time intervals
3. Repeat the experiment (at least once more) for each concentration and calculate a mean
4. Identify and exclude anomalous results before calculating the mean
5. Plot / describe plotting the volume of gas against time to compare the two concentrations, or state the expected trend (higher concentration gives a faster rate / greater volume collected in the same time)

## 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-rate-442c6120) · Published by Druglandscape Ltd.