Advanced Half-Equations
Ionic Half-Equations for Electrolysis · Supplement Level · 15 Questions · 35 Marks
Section A
Halogens
Section B
Hydroxide & O₂
Section C
Active Electrodes
🔑 The Golden Rule: OIL RIG
Oxidation Is Loss of electrons | Reduction Is Gain of electrons. The Anode = Oxidation (electrons leave). The Cathode = Reduction (electrons arrive).
Electrolysis of molten lead(II) bromide using inert carbon electrodes.
Construct the ionic half-equation for the reaction at the anode during the electrolysis of molten lead(II) bromide.
Electrolysis of concentrated hydrochloric acid using inert electrodes.
Write the ionic half-equation for the discharge of chloride ions at the anode.
Electrolysis of molten potassium iodide (KI) using inert graphite electrodes.
Write the ionic half-equation at the anode and state the product formed.
Electrolysis of molten sodium chloride.
Write the ionic half-equation for the reaction at the anode and identify the type of reaction occurring.
A student electrolyses dilute sulfuric acid. At the anode, a colourless gas is produced that relights a glowing splint.
(a) Identify the gas produced at the anode. (b) Write the ionic half-equation for its formation from hydroxide ions.
Electrolysis of dilute sodium hydroxide solution using inert platinum electrodes.
Construct the ionic half-equation for the formation of oxygen at the anode from hydroxide ions.
Electrolysis of copper(II) sulfate solution using inert electrodes.
Write the half-equation for the reaction at the anode. Explain in terms of electron transfer why this is oxidation.
A student electrolyses water acidified with sulfuric acid.
Write the ionic half-equation for the production of oxygen at the anode.
Paper 4 style extended question on electrolysis of brine (concentrated NaCl).
Brine contains Cl⁻, OH⁻, Na⁺, and H⁺ ions. Explain which ions are discharged at the anode and write the half-equation.
Electrolysis of dilute sulfuric acid.
At the anode, oxygen is produced. Balance the following half-equation: OH⁻ → H₂O + O₂ + e⁻
Electrolysis of copper(II) sulfate solution using copper electrodes.
Write the half-equation for the reaction at the ANODE when using a copper electrode.
Industrial purification of copper by electrolysis.
(a) Write the half-equation at the anode (impure copper). (b) Write the half-equation at the cathode. (c) State the overall effect on the mass of each electrode.
Electroplating a steel spoon with silver using silver nitrate solution and a silver anode.
Write the half-equation for the reaction at the silver anode.
A student connects a zinc anode to a zinc sulfate solution.
(a) Write the half-equation at the zinc anode. (b) Identify whether this is oxidation or reduction. (c) Use OIL RIG to justify your answer.
Paper 4 Synoptic Question: A student electrolyses copper(II) sulfate with INERT electrodes, then repeats with COPPER electrodes.
Compare the half-equations at the anode for BOTH experiments. Explain the difference in terms of electrode material.
📋 Quick Reference: Half-Equation Checklist
Write the correct ions / atoms as reactants
Write the correct products on the right side
Balance atoms (use coefficients)
Balance charges (add electrons to correct side)
Electrons go RIGHT for oxidation, LEFT for reduction
State whether it is oxidation or reduction using OIL RIG
Cambridge IGCSE Chemistry 0620 · Syllabus 2026–2028 · Limitless Chemistry Professor
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