Chemistry 5070 · O Level · Electrolysis

Electrolysis — practice question

Copper(II) sulfate is classified as an ionic compound.
(a)[2]

Describe how the ions are arranged and what type of attractive forces act between them in solid copper(II) sulfate.

(b)[2]

Explain why solid copper(II) sulfate is a non-conductor, whereas aqueous copper(II) sulfate does conduct electricity.

(c(i))[1]

State where the hydroxide ions come from.

(c(ii))[1]

Complete the equation for the reaction at the positive electrode: $\ldots\text{OH}^- \rightarrow \text{O}_2 + \ldots\text{H}_2\text{O} + \ldots$

(c(iii))[1]

Suggest why hydroxide ions, rather than sulfate ions, are discharged at the positive electrode.

(d(i))[1]

Give the formulae for the four ions found in aqueous copper(II) sulfate.

(d(ii))[2]

Suggest why the solution turns acidic as electrolysis continues.

(d(iii))[1]

Suggest why the blue colour of aqueous copper(II) sulfate gradually fades during electrolysis.

(e)[2]

Draw a ‘dot-and-cross’ diagram for an oxygen molecule. Include only the outer-shell electrons.

Worked solution & mark scheme

This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: Orderly / lattice-like / systematic / regularly spaced / evenly arranged / repeating pattern

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