Practise Electrolysis of molten ionic compounds. 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Name the product formed at the negative electrode (cathode).
lead
Molten sodium chloride is electrolysed. Write the half equation for the reaction at the negative electrode.
Na+ + e− → Na
When a molten metal halide is electrolysed using inert electrodes, one product always forms at each electrode. State what is always produced at the negative electrode.
the metal
Electrolysis experiments usually use inert electrodes. Name two materials commonly used as inert electrodes.
graphite (carbon) and platinum
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
A teacher electrolysed molten lead bromide using inert electrodes in a fume cupboard.
(a) Name the product formed at the negative electrode (cathode).[1]
(b) Name the product formed at the positive electrode (anode).[1]
(c) Describe what the teacher would see at the positive electrode.[1]
(d) Explain why the lead bromide must be molten.[1]
Show the answer and mark scheme
(a)Answer: lead
lead
(b)Answer: bromine
bromine
(c)
(red-)brown / orange-brown vapour / gas
(d)
so that the ions are free to move
Question 2Medium3 marks
Molten ionic compounds must be heated to very high temperatures (often several hundred °C) before they can be electrolysed.
(a) Explain why the compound must be molten, rather than solid, for electrolysis to work.[2]
(b) Suggest one practical difficulty of electrolysing a molten ionic compound on an industrial scale.[1]
Show the answer and mark scheme
(a)
ions must be free to move (to the electrodes) to conduct electricity and be discharged
in a solid, the ions are fixed in a lattice and cannot move
(b)
allow: a large amount of energy is needed to melt and maintain the compound at a high temperature (expensive) / special heat-resistant equipment is needed for safety
Question 3Hard6 marks
During electrolysis, reactions at the electrodes can be represented by half equations.
(a) Molten sodium chloride is electrolysed. Write the half equation for the reaction at the negative electrode.[1]
(b) Write the half equation for the reaction at the positive electrode during the electrolysis of molten sodium chloride.[1]
(c) Molten lead bromide is electrolysed. Complete the half equations. Pb2+ + ........ → Pb ....Br− → Br2 + ........[2]
(d) Explain which electrode reaction in the electrolysis of molten lead bromide is oxidation and which is reduction.[2]
Show the answer and mark scheme
(a)Answer: Na+ + e− → Na
Na+ + e− → Na
(b)Answer: 2Cl− → Cl2 + 2e−
2Cl− → Cl2 + 2e−
(c)Answer: Pb2+ + 2e− → Pb; 2Br− → Br2 + 2e−
Pb2+ + 2e− → Pb
2Br− → Br2 + 2e−
(d)
at the negative electrode lead ions gain electrons, so this is reduction
at the positive electrode bromide ions lose electrons, so this is oxidation