The electrolysis of other molten substances
3 marks · NormalA chemist electrolyses molten potassium iodide (KI).
Predict which element is formed at (a) the cathode and (b) the anode. Explain your reasoning in each case.
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Must show: potassium at cathode, iodine at anode, explanation for both
Also accept: K formed at cathode; I2 at anode, with correct explanation
Common mistakes: Mixing up cathode/anode products; Not giving explanations; Incorrectly giving ions instead of elements
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States potassium is formed at the cathode (or K)
B2 · 1 mark · States iodine is formed at the anode (or I2)
E1 · 1 mark · Provides correct explanations for both: K+ ions are reduced at cathode, I- ions are oxidised at the anode
Worked solution
At the cathode: potassium is formed because K+ ions gain electrons (are reduced) to form K atoms.
At the anode: iodine is formed because I- ions lose electrons (are oxidised) to form I2.