A student investigates which powder is the best catalyst for the decomposition of hydrogen peroxide solution.
The student adds 0.50 g of a powder to 25 cm3\mathrm{cm^{3}}cm3 of hydrogen peroxide solution and measures the volume of oxygen collected in 60 seconds.
After each reaction, the student filters off the powder, dries it and weighs it again. The student also does the experiment with no powder.
The table shows the results.
| Powder added | Volume of oxygen collected in 60 s (cm3\mathrm{cm^{3}}cm3) | Mass of powder at start (g) | Mass of powder at end (g) |
|---|---|---|---|
| none | 2 | – | – |
| copper(II) oxide | 22 | 0.50 | 0.50 |
| manganese(IV) oxide | 68 | 0.50 | 0.50 |
| zinc oxide | 3 | 0.50 | 0.50 |
The student keeps the mass of powder the same in each experiment.
State two other variables the student must keep the same.
Which powder is the most effective catalyst?
Explain how the results show that this powder is a catalyst.
Another student says, "The results prove that zinc oxide is a catalyst for this reaction."
Evaluate this statement.
Without a catalyst, the activation energy for this reaction is about 75 kJ/mol. With manganese(IV) oxide, the activation energy is about 58 kJ/mol.
Explain how manganese(IV) oxide increases the rate of the reaction. Use ideas about activation energy and collisions.
The student leaves two flasks until the reactions stop. Flask A has manganese(IV) oxide and flask B has no powder. Both flasks contain the same volume of the same hydrogen peroxide solution.
Compare the total volume of oxygen made in flask A and flask B.
Suggest why the student uses each oxide as a fine powder rather than as lumps.
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.