3.2.3—Periodic trends in redox
- Syllabus
- First assessment 2025
- Objective
- 3.2.3
- Level
- SL
Redox Displacement
A more active metal more readily donates electrons to a less active metal ion. A halogen with greater reduction tendency oxidizes the halide of a weaker halogen.
Test a predicted displacement by placing one metal in the other metal's sulfate or comparing supplied electrode data.
Zinc displaces Cu²⁺ because Zn more readily oxidizes: Zn + Cu²⁺ → Zn²⁺ + Cu. Chlorine displaces Br⁻ because Cl₂ more readily reduces. Keep the metal and halogen trends in their correct electron directions instead of using one vague 'more reactive' rule.
Predicting Displacement Reactions
Assessment in practice
Representative question
Question 1
[Maximum number: 2]
Discuss how the relative reactivity of copper and thallium could be established using the metals and aqueous solutions of their sulfates.
ALTERNATIVE 1:
place thallium in a solution of copper sulfate
if reaction occurs then thallium is more reactive
OR
if no reaction occurs then copper is more reactive
ALTERNATIVE 2:
place copper in a solution of thallium sulfate
if reaction occurs then copper is more reactive
OR
if no reaction occurs then thallium is more reactive
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.