A reaction between two colourless solutions produces a blue substance. A student measures the time taken for the mixture to reach the same shade of blue.
The student tests a solid, X. After each test, the student filters, washes and dries X before weighing it. Each test uses fresh solutions of the same volumes and concentrations, at the same temperature; only the solid used is changed.
| Test | Solid used | Initial mass of X (g) | Final mass of X (g) | Time to reach the same shade of blue (s) |
|---|---|---|---|---|
| 1 | none | – | – | 150 |
| 2 | X | 0.80 | 0.80 | 42 |
| 3 | X recovered from test 2 | 0.80 | 0.80 | 45 |
The student concludes that X is a catalyst for this reaction and will catalyse any reaction that changes colour.
Evaluate the student's conclusion.
122 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.