Worked example
[PLACEHOLDER] Original exam-style question written by Chemify
Question
Molten lead(II) bromide, PbBr₂, is electrolysed using inert electrodes. State what is seen at the anode and write the half-equation for the reaction at the cathode. [2]
Weak answer
0 / 2Bubbles of gas at the anode. Pb → Pb²⁺ + 2e⁻
- Missed B1Bromine is a reddish-brown vapour, not colourless bubbles.
- Missed B1Half-equation is reversed: lead ions gain electrons at the cathode.
Strong answer
2 / 2Anode: reddish-brown vapour (bromine) is given off. Cathode: Pb²⁺ + 2e⁻ → Pb
- Awarded B1Observation includes colour and state.
- Awarded B1Balanced reduction half-equation.
Marks follow the examiner's mark scheme: B = independent mark, M = method/reasoning, A = answer.