Electrolysis and redox
4 marks · NormalThe diagram shows an apparatus used in the electrolysis of molten lead(II) iodide. The electrodes and power supply are labelled.
Explain what is meant by 'discharging an ion' during electrolysis.
State what happens to the lead(II) ions at the cathode, referring to electron transfer.
Write the ionic half-equation for the reaction at the anode.
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.
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(a) Discharging an ion means the ion loses its charge by gaining or losing electron(s) at the electrode.
(b) The lead(II) ions gain electrons to become lead atoms.
(c) 2I^- \rightarrow I_2 + 2e^-
Common mistakes: Describing discharge only as 'losing color' or physical change.; Mixing up which ion is at which electrode.; Using atoms instead of ions in the half-equation.
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Marking points
M1 (a) · 1 mark · States the ion loses or gains electrons at the electrode to lose its charge.
M1 (a) · 1 mark · Explains that this results in a neutral atom or molecule being formed.
B1 (b) · 1 mark · Correctly states that lead(II) ions gain electrons at the cathode (or equivalent wording).
A1 (c) · 1 mark · Correct ionic half-equation for iodide at the anode: 2I^- \rightarrow I_2 + 2e^-
Worked solution
a. Discharging an ion during electrolysis means the ion loses its charge by either gaining or losing electron(s) at the electrode, resulting in a neutral atom or molecule.
b. Lead(II) ions at the cathode gain electrons to form lead atoms.