4.14 Electrolysis of aqueous solutions
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Which gas forms at the anode when copper sulfate solution is electrolysed with inert electrodes?
Choose one answer.
Correct Not quite: the answer is Oxygen
Mark scheme
B
Model answer
B: there are no halide ions, so oxygen forms.
Potassium bromide solution is electrolysed.
Name the products at the cathode and at the anode. Explain the cathode product.
Mark scheme
- cathode: hydrogen (1)
- because potassium is more reactive than hydrogen (1)
- anode: bromine (1)
Model answer
Hydrogen forms at the cathode because potassium is more reactive than hydrogen. Bromine forms at the anode because bromide ions are present.
Name the three products of electrolysing sodium chloride solution.
Mark scheme
- hydrogen (1)
- chlorine (1)
- sodium hydroxide (1)
Model answer
Hydrogen, chlorine and sodium hydroxide.
Explain why copper, not hydrogen, forms at the cathode when copper chloride solution is electrolysed.
Mark scheme
- copper is less reactive than hydrogen (1)
- so copper ions are discharged / gain electrons in preference (1)
Model answer
Copper is less reactive than hydrogen, so copper ions gain electrons more readily than hydrogen ions and copper is deposited.
Where do the hydrogen ions and hydroxide ions in an aqueous solution come from?
Mark scheme
- water (1)
Model answer
They come from the water, which ionises very slightly.
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