Charge Flow in Electrolysis
Cambridge IGCSE Chemistry 0620 • Electrolysis (Section 4.1)
Circuit Diagram
Electrolysis cell — electrons flow through external circuit; ions migrate through electrolyte
Attempt each question, then reveal the mark scheme answer.
Destinations
At which electrode are metals deposited during electrolysis?
Think: metals are positive ions that gain electrons.
At which electrode are non-metals formed during electrolysis?
Non-metals form from negative ions losing electrons.
During electrolysis of copper(II) sulfate solution using copper electrodes, what forms at the cathode?
Which positive ions are present in solution?
During electrolysis of dilute sulfuric acid, what gas is produced at the anode?
What negative ions are present? What do they form when discharged?
During electrolysis of molten lead(II) bromide (PbBr₂), identify the product at each electrode.
Identify which ions go to which electrode.
Conduction Mechanism
Describe how charge is transferred through the external circuit (the wires and battery) during electrolysis.
Metals conduct electricity differently from solutions.
Describe how charge is transferred through the electrolyte during electrolysis.
The electrolyte is a liquid — what charged particles can move?
Why must an ionic compound be molten or dissolved in water (aqueous) to conduct electricity?
Think about the state of the ions in a solid ionic compound.
Compare how metals conduct electricity with how electrolytes conduct electricity.
Two types of charge carriers — which is which?
Explain why the concentration of an electrolyte affects the conductivity of the solution.
More ions = more charge carriers.
Explanations
Explain how charge is transferred at the cathode during electrolysis. Include a half-equation using a suitable example.
Positive ions arrive at the negative electrode. What must happen to them?
Explain how charge is transferred at the anode during electrolysis. Include a half-equation using a suitable example.
Negative ions arrive at the positive electrode. What happens to them?
During electrolysis of concentrated sodium chloride solution, chlorine is produced at the anode rather than oxygen. Explain why.
Both Cl⁻ and OH⁻ are present. Which is preferentially discharged?
A student electrolyses copper(II) sulfate solution using inert (graphite) electrodes. Describe and explain the changes observed at both electrodes over time.
Track what happens to Cu²⁺ ions and to water as the electrolysis proceeds.
Explain the industrial importance of the electrolysis of brine (concentrated sodium chloride solution), naming the three products and a use for each.
Three products form at the two electrodes and in the remaining solution.
Quick Reference — OIL RIG
OXIDATION (Anode +)
Is Loss of electrons
Anions → lose e⁻ → neutral
e.g. 2Cl⁻ → Cl₂ + 2e⁻
REDUCTION (Cathode −)
Is Gain of electrons
Cations → gain e⁻ → neutral
e.g. Cu²⁺ + 2e⁻ → Cu
CHARGE TRANSFER SUMMARY
External circuit (wires): electrons flow
Electrolyte (liquid): ions migrate
Cambridge IGCSE Chemistry 0620 • Electrolysis 4.1.4 • Charge Flow Exam
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