Practise 29 exam-style questions on Electrolysis of aqueous solutions for AQA GCSE Chemistry. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.
29 questions
1–6 marks each
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20 questions, marked as you go
Sample questions with model answers
Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.
Question 1
2 marks
Copper(II) sulfate solution is electrolysed using inert electrodes.
Name the product formed at each electrode.
Model answer
Copper is formed at the cathode and oxygen at the anode.
Explanation
Copper is less reactive than hydrogen, so copper ions are discharged at the cathode. Sulfate is not a halide, so hydroxide ions from water are discharged at the anode, giving oxygen.
Mark scheme
1 mark
cathode: copper
1 mark
anode: oxygen
do not accept sulfur, sulfur dioxide or sulfate
Question 2
2 marks
Which one of these solutions would produce oxygen at the anode when electrolysed using inert electrodes? Give a reason for your answer.
Copper(II) sulfate solution, because it is the only solution that does not contain halide ions; the others would produce chlorine, iodine or bromine at the anode.
Explanation
Oxygen is only produced at the anode when there are no halide ions. Chloride, bromide and iodide ions are all halide ions, so they produce the halogen instead.
Mark scheme
1 mark
copper(II) sulfate solution
1 mark
it is the only one that does not contain halide ions
allow the others contain chloride, iodide or bromide ions, which produce halogens
Question 3
3 marks
During the electrolysis of copper(II) sulfate solution, copper is deposited on the cathode.
Write a half equation for this reaction. State whether the copper ions are oxidised or reduced, and give a reason.
Model answer
Cu²⁺ + 2e⁻ → Cu The copper ions are reduced, because they gain electrons.
Explanation
Reactions at the cathode are always reductions, because positive ions gain electrons there. Copper(II) ions have a 2+ charge, so each needs two electrons.
Mark scheme
1 mark
Cu²⁺ + 2e⁻ → Cu
allow Cu2+ + 2e- → Cu; ignore state symbols
1 mark
reduced
1 mark
because they gain electrons
Question 4
4 marks
Sodium chloride can be electrolysed when molten or when dissolved in water.
Compare the products formed in each case. Explain why the products are different.
Model answer
When molten sodium chloride is electrolysed, sodium forms at the cathode and chlorine at the anode. When sodium chloride solution is electrolysed, hydrogen forms at the cathode and chlorine at the anode. The solution also contains H⁺ ions from water, and because sodium is more reactive than hydrogen, the H⁺ ions are discharged at the cathode instead of the Na⁺ ions. Chlorine forms at the anode in both cases because chloride ions are present.
Explanation
In a molten binary compound only two kinds of ion are present, so the products are always the two elements. In water, H⁺ and OH⁻ ions compete, and the reactivity rules decide which ions are discharged.
Mark scheme
1 mark
molten: sodium at the cathode and chlorine at the anode
1 mark
aqueous: hydrogen at the cathode and chlorine at the anode
1 mark
in solution there are also hydrogen ions from the water
1 mark
sodium is more reactive than hydrogen, so hydrogen ions are discharged instead of sodium ions
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