A student repeats a sodium thiosulfate experiment four times and records the time for the cross to disappear.
| Repeat | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| Time (s) | 42 | 44 | 61 | 43 |
The student ignores any anomalous result and calculates the mean time. The student then uses rate = 1mean time\dfrac{1}{\text{mean time}}mean time1.
What is the rate of reaction?
0.021 s−10.021\,\mathrm{s^{-1}}0.021s−1
0.023 s−10.023\,\mathrm{s^{-1}}0.023s−1
23 s−123\,\mathrm{s^{-1}}23s−1
43 s−143\,\mathrm{s^{-1}}43s−1
56 exam-style questions on OCR GCSE Chemistry 5.2 Controlling reactions, covering 5.2.1 Measuring and interpreting rate of reaction, 5.2.2 Factors affecting rate and collision theory, and 5.2.3 Catalysts, activation energy and enzymes. Each one has a worked solution and a mark scheme showing where the marks go.