Two solutions, P and Q, react to form a blue product. A student investigates the effect of the concentration of solution P on the rate of reaction. The student records the time taken for each mixture to reach the same shade of blue. The same shade is reached when the same amount of blue product has formed.
| Experiment | Concentration of P in mol/dm³ | Volume of P in cm³ | Concentration of Q in mol/dm³ | Volume of Q in cm³ | Temperature in °C | Time in s |
|---|---|---|---|---|---|---|
| 1 | 0.20 | 20 | 0.50 | 20 | 25 | 52 |
| 2 | 0.40 | 20 | 0.50 | 20 | 25 | 27 |
| 3 | 0.40 | 20 | 0.50 | 20 | 35 | 16 |
Give the numbers of the two experiments that should be compared to investigate the effect of the concentration of solution P. Calculate the ratio of the relative rate in the faster experiment to the relative rate in the slower experiment.
A student calculates that the relative rate in experiment 3 is about 3.3 times the relative rate in experiment 1. The student concludes that this difference is caused only by the concentration of solution P. Explain why this conclusion is not valid.
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.