A student places a flask of dilute hydrochloric acid on a balance and adds marble chips. A loose plug of cotton wool is put in the neck of the flask.
CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)\mathrm{CaCO_{3}(s)} + \mathrm{2HCl(aq)} \rightarrow \mathrm{CaCl_{2}(aq)} + \mathrm{H_{2}O(l)} + \mathrm{CO_{2}(g)}CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)
The table shows the total loss in mass of the flask and contents.
| Time in min | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|---|
| Loss in mass in g | 0.00 | 0.40 | 0.66 | 0.80 | 0.86 | 0.88 | 0.88 |
Explain why the mass of the flask and contents decreases.
Suggest the purpose of the cotton wool.
Calculate the mean rate of reaction in the first 2 minutes. Give the unit.
Explain, in terms of particles, why the rate of reaction decreases during the experiment.
Calculate the mass of calcium carbonate that reacted. Relative formula masses: CaCO3=100,CO2=44\mathrm{CaCO_{3}} = 100, \mathrm{CO_{2}} = 44CaCO3=100,CO2=44
54 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.