Copper used for electrical wiring must be very pure. Impure copper can be purified by electrolysis.
The anode is a block of impure copper. The cathode is a thin sheet of pure copper. The electrolyte is copper sulfate solution.
Write the half equation for the reaction of copper at the anode.
In one experiment, the only impurities in the anode are silver and gold. These collect as a solid below the anode.
The table shows the results.
| Measurement | Mass (g) |
| :---: | :---: |
| decrease in mass of the anode | 20.00 |
| increase in mass of the cathode | 19.40 |
| mass of solid collected below the anode | 0.60 |
Calculate the percentage by mass of copper in the impure anode.
Give your answer to 3 significant figures.
Explain why silver and gold collect as a solid below the anode.
A different block of impure copper contains zinc as an impurity.
No zinc is found in the solid below the anode, and no zinc forms on the cathode.
Explain these observations.
When the anode contains zinc, the concentration of copper ions in the electrolyte slowly decreases.
Explain why.
52 exam-style questions on OCR GCSE Chemistry 3.4 Electrolysis, covering 3.4.1 Products formed at the electrodes in electrolysis and 3.4.2 The technique of electrolysis. Each one has a worked solution and a mark scheme showing where the marks go.