A refinery uses this arrangement to purify copper recovered from old electrical cables. The impure copper slab is connected to the positive electrode and a ...
Question 1 Report
A refinery uses this arrangement to purify copper recovered from old electrical cables. The impure copper slab is connected to the positive electrode and a thin sheet of pure copper is connected to the negative electrode. Both electrodes are placed in copper sulfate solution. Fig. 1 includes particles that have settled beneath the positive electrode after several hours. The refinery wants copper of high purity for making electrical wires.
(a) Name the electrode at which pure copper is deposited. [2]
(b) State the change in mass of the impure copper slab during electrolysis. [2]
(c) Complete the ionic equation for the reaction occurring at the positive electrode.
Cu → Cu2+ + ........ [3]
(d) Give the equation for the reaction at the negative electrode. [3]
(e) Explain why insoluble impurities collect at the bottom of the cell instead of coating the pure copper sheet. [3]
(f) State one property of copper that makes purified copper suitable for electrical wires. [3]
Answer Details
(a) Pure copper is deposited on the negative electrode, the cathode. [2]
(b) The mass of the impure copper slab decreases because copper atoms leave the slab and enter solution as copper ions. [2]
(c) \[\mathrm{Cu\rightarrow Cu^{2+}+2e^-}\]
Copper atoms are oxidised at the positive electrode. [3]
(d) \[\mathrm{Cu^{2+}+2e^-\rightarrow Cu}\]
Copper(II) ions are reduced and form pure copper at the negative electrode. [3]
(e) Insoluble impurities do not form ions or dissolve in the solution. They fall from the impure copper slab to the bottom, while copper ions are reduced and deposited on the negative electrode instead. [3]
(f) Copper is a good electrical conductor, is ductile so can be drawn into wires, has a high melting point and does not react readily. Any three. [3]
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