The electrolysis of some other solutions using inert electrodes
5 marks · HardA student electrolyses separate aqueous solutions containing different anions using inert electrodes.
State which ion produces oxygen gas at the anode when an aqueous solution of sodium sulfate is electrolysed.
Explain why oxygen is produced at the anode during this electrolysis and not another gas.
During the electrolysis of aqueous sodium chloride with inert electrodes, state the product formed at the anode. Explain your answer.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Hydroxide ion | OH⁻
(b) Oxygen is produced because sulfate ions are too difficult to oxidise, so hydroxide ions are discharged.
(c) Chlorine is formed at the anode; chloride ions discharge because halide ions are oxidised in preference to hydroxide ions at the anode.
Common mistakes: Stating sulfate instead of hydroxide for oxygen production.; Stating that all anions produce oxygen.; Stating that oxygen forms at the anode for chloride.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Hydroxide ion (OH⁻) correctly identified for production of oxygen at the anode.
B2 (b) · 1 mark · States that sulfate ions are too difficult to oxidise or not discharged/preference for hydroxide ions.
B3 (b) · 1 mark · States that hydroxide ions are discharged to produce oxygen.
B4 (c) · 1 mark · Chlorine correctly identified as the anode product for sodium chloride solution.
B5 (c) · 1 mark · Explains that halide ions (chloride) are discharged in preference to hydroxide ions.
Worked solution
a) Hydroxide ions (OH⁻) produce oxygen at the anode.
b) During the electrolysis of sodium sulfate, sulfate ions are too difficult to oxidise. Therefore, hydroxide ions from the water are discharged at the anode to give oxygen gas.
c) During electrolysis of aqueous sodium chloride, chloride ions are discharged at the anode because halide ions are oxidised in preference to hydroxide ions. Therefore, chlorine gas is formed at the anode.