# A student investigates whether the concentration of hydrochloric acid affects the rate of its reaction with zinc powder. Describe how the student could carry out a fair and valid experiment to investigate this.

> Cambridge International IGCSE Chemistry (0620) — 12.1 Experimental design · Describe · 4 marks

## Mark scheme (4 marks)

1. Use the same mass / amount of zinc powder in each experiment
2. Change only the concentration of hydrochloric acid between experiments (while keeping volume the same)
3. Control all other variables — e.g. temperature, volume of acid, or particle size of zinc kept constant
4. Measure the rate of reaction — e.g. measure the time taken for a given volume of gas to be produced, or time for the reaction to finish, or measure volume of gas produced in a set time

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-investigates-whether-the-concentration-5ece3039) · Published by Druglandscape Ltd.