A blue solution reacts with a colourless solution, X, and the blue colour fades. A student investigates the effect of the concentration of X on the rate of reaction.
The student mixes fixed volumes of the two solutions and records the time taken for the mixture to reach the same pale-blue endpoint. The temperature and all other conditions are kept constant.
| Concentration of X in mol dm−3\mathrm{mol\,dm^{-3}}moldm−3 | Time in repeat 1 in s | Time in repeat 2 in s | Time in repeat 3 in s |
|---|---|---|---|
| 0.150 | 124 | 120 | 122 |
| 0.300 | 64 | 62 | 91 |
Calculate the relative rate for each concentration of X. Give your answers in s−1\mathrm{s^{-1}}s−1. Use the repeat measurements to decide whether any result should be omitted.
The student concludes that doubling the concentration of X doubles the relative rate of reaction.
Evaluate this conclusion using the results.
Explain how the particle behaviour in the mixtures accounts for the faster reaction at the higher concentration.
122 exam-style questions on Edexcel GCSE Chemistry 8.1 Rates of reaction, covering 8.1.1 Measuring and interpreting rates of reaction, 8.1.2 Collision theory and the factors affecting rate, and 8.1.3 Catalysts and enzymes. Each one has a worked solution and a mark scheme showing where the marks go.