When molten potassium iodide is electrolysed, potassium forms at the negative electrode. When potassium iodide solution is electrolysed, hydrogen forms at the negative electrode instead.
Why can hydrogen form from the solution but not from the molten compound?
The solution contains hydrogen ions from water, but the molten compound does not
Hydroxide ions in the solution move to the negative electrode and form hydrogen
Hydrogen gas dissolved in the water is released at the negative electrode
Electrons flow through the solution and split the water molecules into hydrogen
76 exam-style questions on AQA GCSE Chemistry 4.3 Electrolysis, covering 4.3.1a The process of electrolysis, 4.3.1b Half equations in electrolysis, 4.3.2 Electrolysis of molten ionic compounds, 4.3.3 Using electrolysis to extract metals, 4.3.4 Electrolysis of aqueous solutions, and 4.3.5 Representation of reactions at electrodes as half equations. Each one has a worked solution and a mark scheme showing where the marks go.