Electrolysis — GCSE Chemistry practice questions

Question 1

A technician electrolyses molten calcium bromide using graphite electrodes.

Which row names the product at each electrode?

Accepted Answer

B: calcium · bromine. Molten calcium bromide contains only Ca²⁺ and Br⁻ ions. The metal, calcium, forms at the cathode and the non-metal element, bromine, forms at the anode.

Question 2

Aqueous silver nitrate is electrolysed using graphite electrodes.

Which row is correct?

Accepted Answer

D: silver · oxygen. Silver is less reactive than hydrogen, so silver ions gain electrons and silver forms at the cathode. Nitrate ions are not discharged, so oxygen forms at the anode from the hydroxide ions of water.

Question 3

Aqueous copper(II) nitrate is electrolysed twice.

- Experiment 1: graphite electrodes
- Experiment 2: copper electrodes

Which row is correct?

Accepted Answer

B: bubbles of gas · loses mass · stays the same. With graphite, oxygen bubbles form at the anode. With copper, the anode atoms lose electrons and go into solution as Cu²⁺ ions, so the anode loses mass. These ions replace the ones deposited at the cathode, so the blue colour stays the same.

	cathode	anode
A	calcium	bromide
B	calcium	bromine
C	bromine	calcium
D	hydrogen	bromine

	anode in experiment 1	anode in experiment 2	blue colour of the solution in experiment 2
A	bubbles of gas	gains mass	fades
B	bubbles of gas	loses mass	stays the same
C	gains mass	loses mass	stays the same
D	bubbles of gas	bubbles of gas	fades