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3.2.15 (HL)—Electrolysis of aqueous solutions

Syllabus
First assessment 2025
Objective
3.2.15
Level
HL

Aqueous Electrolysis

HL only

At each electrode compare the possible aqueous species using reduction or oxidation tendencies. Water may react instead of sulfate or in dilute halide solution; concentrated halide can be oxidized, while molten salt contains no water.

List the solute ion and water as competing possibilities at each electrode, then use electrode-potential data together with stated concentration conditions to select products. In aqueous sulfate, water commonly supplies the anode gas; in concentrated halide, halogen formation may compete. Do not transfer molten-salt products automatically to solution.

Selecting Aqueous-Electrolysis Products

HL only

Assessment in practice

Representative question

Question 1

[Maximum number: 2]

Determine the products formed at each electrode during the electrolysis of an aqueous solution of sodium bromide. Use section 24 in the data booklet.

Positive electrode (anode):
Negative electrode (cathode):

Electron Transfer Reactions Summary

Retrieve the route: assign oxidation states, balance half-equations, predict displacement, label cells, trace electrons and ions, follow organic redox pathways, calculate potentials and choose electrolysis products.

Check electron loss/gain, anode/cathode versus polarity, spontaneous sign, salt-bridge direction, ions present, organic functional-group direction and object-cathode placement.