4.12 Electrolysis of molten ionic compounds
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To which electrode are positive ions attracted during electrolysis?
Choose one answer.
Correct Not quite: the answer is The cathode
Mark scheme
A
Model answer
A: positive ions move to the negative electrode, the cathode.
Explain why solid lead bromide does not conduct electricity, but molten lead bromide does.
Mark scheme
- in the solid the ions are fixed / cannot move (1)
- when molten the ions are free to move (and carry charge) (1)
Model answer
In the solid the ions are held in fixed positions in the lattice; when molten the ions are free to move and carry the current.
Molten potassium iodide is electrolysed.
Name the products at the cathode and at the anode.
Mark scheme
- cathode: potassium (1)
- anode: iodine (1)
Model answer
Potassium forms at the cathode and iodine at the anode.
Explain why the electrodes used in electrolysis are often made of graphite.
Mark scheme
- graphite conducts electricity (1)
- it is inert / unreactive / has a high melting point (1)
Model answer
Graphite conducts electricity and is inert, so it does not react with the electrolyte or the products.
During the electrolysis of molten lead bromide, describe what happens to the bromide ions.
Mark scheme
- bromide ions move to the anode (1)
- they lose electrons to form bromine (1)
Model answer
The negative bromide ions are attracted to the positive anode, where they lose electrons and form bromine gas.
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