With respect to the electrolysis of copper (II) sulphate solution using copper electrodes, which statement is correct?
(a) Copper metal is deposited at the negative electrode.
(b) Oxygen gas is produced at the positive electrode.
(c) The positive electrode increases in mass.
(d) The negative electrode decreases in mass.
(a) Copper metal is deposited at the negative electrode.
Explanation –
During electrolysis of copper(II) sulphate solution using copper electrodes:
At the cathode (negative electrode): \mathrm{Cu^{2+}} + 2\mathrm{e^-} \rightarrow \mathrm{Cu}, so copper is deposited here and the cathode increases in mass.
At the anode (positive electrode): \mathrm{Cu} - 2\mathrm{e^-} \rightarrow \mathrm{Cu^{2+}}, so copper of the anode dissolves and the anode decreases in mass.
No oxygen gas is produced because the copper is preferentially oxidised over the OH− ions.
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