The electrolysis of some other solutions using inert electrodes
4 marks · NormalPotassium chloride solution is electrolysed using inert electrodes.
State whether hydrogen or potassium is formed at the cathode.
Explain why this product is formed at the cathode, using the reactivity series.
Name the product formed at the anode.
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(a) Hydrogen
(b) Potassium is above hydrogen in the reactivity series, so hydrogen ions are preferentially discharged at the cathode, releasing hydrogen gas. · must show Potassium more reactive than hydrogen, Hydrogen discharged in preference at cathode
(c) Chlorine
Common mistakes: Saying potassium is produced at the cathode
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Marking points
B1 (a) · 1 mark · Identifies hydrogen as the product at the cathode.
M1 (b) · 1 mark · States that potassium is more reactive than hydrogen OR use of reactivity series.
A1 (b) · 1 mark · States that hydrogen is therefore discharged in preference at the cathode.
B2 (c) · 1 mark · Identifies chlorine as the product at the anode.
Worked solution
a) Hydrogen is formed at the cathode.
b) Potassium is above hydrogen in the reactivity series, so potassium ions are not discharged. Instead, hydrogen ions (from water) are preferentially discharged, releasing hydrogen gas.
c) Chlorine is formed at the anode.