The electrolysis of molten compounds
4 marks · NormalThe diagram below shows the electrolysis of molten copper(II) bromide (CuBr2) using carbon electrodes.
Identify the ions present in molten copper(II) bromide.
State what is produced at the cathode and at the anode.
Write the half-equation for the reaction at the cathode.
Describe a visible change that would be observed at the anode during electrolysis.
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) Copper(II) ions (Cu^{2+}) and bromide ions (Br^-)
(b) Copper metal at the cathode; bromine gas at the anode
(c) Cu^{2+} + 2e^- → Cu
(d) Brown vapour (bromine gas) is released at the anode
Common mistakes: Swapping cathode and anode reactions; Forgetting charge on copper(II) ion
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Marking points
B1 (a) · 1 mark · States copper(II) ions (Cu^{2+}) and bromide ions (Br^-) present
B2 (b) · 1 mark · Identifies copper at the cathode, bromine at the anode
B3 (c) · 1 mark · Correct cathode half-equation: Cu^{2+} + 2e^- → Cu
B4 (d) · 1 mark · Describes brown vapour (bromine) seen at the anode
Worked solution
(a) The ions present are copper(II) ions (Cu^{2+}) and bromide ions (Br^-).
(b) Copper metal forms at the cathode; bromine gas forms at the anode.
(c) Half-equation at the cathode: Cu^{2+} + 2e^- → Cu
(d) Brown vapour is seen at the anode, as bromine gas forms.