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
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Discuss how the relative reactivity of copper and thallium could be established using the metals and aqueous solutions of their sulfates.
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.