Passing electricity through compounds: electrolysis
2 marks · HardA student investigates the electrolysis of molten lead(II) bromide () using inert electrodes.
State one observation the student would make at each electrode during this experiment.
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Also accept: At the cathode: grey solid/metallic lead forms; At the anode: brown gas/orange vapour/bubbles (bromine gas) observed
Common mistakes: Naming chlorine at anode instead of bromine; Saying 'gas at cathode'; Not specifying observable changes
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Marking points
B1 · 1 mark · States that metallic lead or a grey solid forms at the cathode
B2 · 1 mark · States that a brown/orange vapour (bromine gas) or bubbles are seen at the anode
Worked solution
At the cathode, metallic lead forms and may be visible as a grey solid deposit.
At the anode, bromine gas is produced, which appears as a brown/orange vapour or bubbles at the electrode.