A student adds marble chips (calcium carbonate) to dilute hydrochloric acid in a conical flask on a balance.
The student puts a loose plug of cotton wool in the neck of the flask.
CaCO3+2HCl→CaCl2+H2O+CO2 \mathrm{CaCO_{3}} + 2\mathrm{HCl} \rightarrow \mathrm{CaCl_{2}} + \mathrm{H_{2}O} + \mathrm{CO_{2}} CaCO3+2HCl→CaCl2+H2O+CO2The table shows the results.
| Time (min) | Mass of flask and contents (g) |
|---|---|
| 0 | 150.00 |
| 1 | 149.40 |
| 2 | 149.00 |
| 3 | 148.74 |
| 4 | 148.60 |
| 5 | 148.56 |
| 6 | 148.56 |
At the end of the reaction, some marble chips are left in the flask.
Explain why the mass of the flask and contents decreases.
Suggest why the student uses a cotton wool plug.
Calculate the total mass of carbon dioxide given off.
Mass = ...... g
Calculate the mean rate of reaction in the first 2 minutes.
Use the equation: mean rate of reaction = mass lost ÷ time
Mean rate = ...... g/min
The rate of reaction decreases as the reaction goes on.
Explain why. Use ideas about particles and collisions.
The student repeats the experiment with the same mass of marble powder instead of marble chips. Everything else stays the same.
Describe how the results would be different.
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.