The electrolysis of copper(ii) sulfate solution using inert electrodes
2 marks · NormalExplain why oxygen gas is produced at the anode during the electrolysis of copper(II) sulfate solution with inert electrodes.
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Sulfate ions are difficult to oxidise, so hydroxide ions from water are discharged at the anode, producing oxygen gas.
Also accept: OH- ions are more easily oxidised than sulfate ions
Common mistakes: Saying sulfate gives oxygen
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Marking points
M1 · 1 mark · Mentions sulfate ions are not oxidised at the anode
A1 · 1 mark · States that hydroxide ions are oxidised, forming oxygen gas
Worked solution
At the anode, both sulfate and hydroxide ions are attracted. Sulfate ions are not easily oxidised, so hydroxide ions from water are discharged instead. The oxidation of hydroxide ions produces oxygen gas.