Required Practical: Rate of Reaction

This lesson covers the AQA GCSE Combined Science Trilogy (8464) required practical on investigating how changing concentration (or temperature) affects the rate of reaction. You must be able to describe the method, identify variables, interpret results, and evaluate the experiment. This practical is commonly examined on both papers.

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Overview of the Practical

There are two common versions of this required practical:

1. Sodium thiosulfate and hydrochloric acid (disappearing cross) — investigating the effect of concentration or temperature.
2. Marble chips (calcium carbonate) and hydrochloric acid — investigating the effect of concentration using gas collection.

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Practical 1: Sodium Thiosulfate and Hydrochloric Acid

The Reaction

$\text{Na}_2\text{S}_2\text{O}_3\text{(aq)} + 2\text{HCl(aq)} \rightarrow 2\text{NaCl(aq)} + \text{S(s)} + \text{SO}_2\text{(g)} + \text{H}_2\text{O(l)}$Na2​S2​O3​(aq)+2HCl(aq)→2NaCl(aq)+S(s)+SO2​(g)+H2​O(l)

The sulfur produced is a yellow precipitate that makes the solution go cloudy.

Method (Investigating Concentration)