3.2.1—Oxidation and reduction
- Syllabus
- First assessment 2025
- Objective
- 3.2.1
- Level
- HL
Oxidation and Reduction
Oxidation is loss of electrons and an increase in oxidation state; reduction is gain of electrons and a decrease. The oxidizing agent is reduced, and the reducing agent is oxidized.
Use the oxidation-state rules and total charge to identify which species changed and which agent caused the change.
In Zn + Cu²⁺ → Zn²⁺ + Cu, Zn rises from 0 to +2 and is oxidized, so it is the reducing agent; Cu²⁺ falls from +2 to 0 and is reduced, so it is the oxidizing agent. Name agents from what happens to them, not from the process they cause in the other species.
Identifying Redox Agents
Assessment in practice
Representative question
Question 1
[Maximum number: 2]
Identify the oxidising and reducing agents, and the species oxidised and reduced, in the forward reaction.
| CO(g) | H2O(g) | |
|---|---|---|
| oxidising or reducing agent? | ||
| species oxidised or reduced? |
\multicolumn{2}{|c|}{& CO(g) & H2O(g)
Oxidising or reducing agent? & reducing & oxidising
Species oxidised or reduced? & oxidised & reduced
\end{tabular}}
Award [1] for every two correct.
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.