A student investigates how the mass of copper deposited on the cathode depends on the time of electrolysis. The student uses two copper electrodes in copper sulfate solution with a constant current. The cathode is weighed before and after each experiment.
The table shows the results.
| Time / min | Mass gained run 1 / g | Mass gained run 2 / g | Mass gained run 3 / g | Mean mass gained / g |
|---|---|---|---|---|
| 5 | 0.05 | 0.04 | 0.06 | 0.05 |
| 10 | 0.10 | 0.11 | 0.09 | 0.10 |
| 15 | 0.14 | 0.16 | 0.23 | ? |
| 20 | 0.20 | 0.21 | 0.19 | 0.20 |
| 25 | 0.25 | 0.24 | 0.26 | 0.25 |
Give the dependent variable in this investigation.
Identify the anomalous result in the table.
Calculate the mean mass gained at 15 minutes.
Suggest one reason for the anomalous result.
Describe the relationship between time and the mass of copper gained by the cathode.
State what happens to the mass of the anode. Explain why the colour of the copper sulfate solution does not change.
52 exam-style questions on Edexcel GCSE Chemistry 4.2 Electrolytic processes, covering 4.2.1 Electrolytes and the process of electrolysis, 4.2.2 Products of electrolysis using inert electrodes, 4.2.3 Half equations, oxidation and reduction in electrolysis, and 4.2.4 Electrolysis of copper sulfate and purifying copper. Each one has a worked solution and a mark scheme showing where the marks go.