Electrolysis of Copper Sulfate

Question 1

Graphite electrodes are an example of inert electrodes.

Explain what is meant by the term ‘inert’ when referring to electrodes.

Answer 1

Inert electrodes are electrodes that do not react with the electrolyte

Question 2

What is produced at the cathode when you electrolyse copper sulfate solution with inert electrodes?

Answer 2

Copper is less reactive than hydrogen in the reactivity series, so copper metal is produced

Question 3

What is produced at the anode when you electrolyse copper sulfate solution with inert electrodes?

Answer 3

There aren’t any halide ions present, so oxygen and water are produced

Question 4

Give the half equation for the product at the cathode when you electrolyse copper sulfate solution with inert electrodes.

Answer 4

Question 5

Give the half equation for the product at the anode when you electrolyse copper sulfate solution with inert electrodes.

Answer 5

Question 6

Explain why the sizes of both the anode and the cathode change.

Answer 6

• Copper atoms from the impure copper anode are oxidised, dissolving into the electrolyte to form copper ions
• Those copper ions are reduced at the pure copper cathode, and add to it as a layer of pure copper

Question 7

Explain why a solid appears directly beneath the anode.

Answer 7

A sludge of impurities from the impure copper anode sink to the bottom

Question 8

Explain why the colour of the copper sulfate solution does not change.

Answer 8

• Copper sulfate solution is blue
• It remains this colour since for every copper ion entering the solution at the anode, one is removed from the solution at the cathode

Question 9

(Exam-style question)

Answer 9