Q53 · Practice questionComplex familiar4 marks
QUESTION 53 (4 marks)
Aqueous copper(II) sulfate is electrolysed using graphite electrodes. Assume copper is deposited and oxygen evolves.
a) Write the cathode and anode half-equations. [2 marks]
b) Predict two changes if the graphite anode is replaced by a copper anode, with all other conditions unchanged. [2 marks]
WORKED SOLUTION
4 marksPractice marking scheme
; ; copper anode dissolves and replenishes copper ions.
At an inert anode water is oxidised. A copper anode instead undergoes Cu → Cu²⁺ + 2e⁻: its mass decreases and, ideally, copper-ion concentration remains approximately constant rather than falling. Oxygen evolution ceases in this ideal model.
- Writes correct cathode half-equation. [1 marks]
- Writes balanced water-oxidation half-equation. [1 marks]
- Predicts copper-anode dissolution/mass decrease. [1 marks]
- Predicts approximately maintained Cu²⁺ concentration or cessation of oxygen evolution. [1 marks]
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