O-Level and SEC G3 Chemistry K324
C7: Redox Chemistry
Track electron transfer and oxidation states. Pure K324 includes electrolysis outcomes that Combined Chemistry does not.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Redox Chemistry uses three compatible lenses: oxygen or hydrogen transfer, electron transfer, and oxidation-state change. Pure K324 then extends into electrolysis, copper purification, electroplating, simple cells, and hydrogen fuel cells, which is an important boundary from the narrower Combined Chemistry component.
Recognising oxidation and reduction
Oxidation can mean gain of oxygen, loss of hydrogen, loss of electrons, or increase in oxidation state. Reduction is the reverse. An oxidising agent causes another substance to be oxidised and is itself reduced; a reducing agent causes reduction and is itself oxidised. State which species changes and use one consistent definition.
Aqueous potassium iodide tests for oxidising agents through iodine formation, while acidified potassium manganate(VII) tests for reducing agents through its colour change. Report initial and final colours from the supplied conditions and do not confuse the testing reagent with the species being identified.
Electrolysis and selective discharge
Electrolysis is electrical conduction through a molten or aqueous ionic compound with chemical change at electrodes. Cations move to the cathode and are reduced; anions move to the anode and are oxidised. Solid ionic compounds do not conduct because ions are fixed. A molten binary compound gives its metal and non-metal products at inert electrodes.
For aqueous electrolytes, predict products from the ions present, the metal reactivity series, anion type, and concentration when relevant. Write half-equations only after selecting products. Concentrated and dilute sodium chloride can give different anode products. Copper(II) sulfate with copper electrodes transfers copper from the impure anode to the pure cathode.
Electroplating, cells and hydrogen
In electroplating, the object is the cathode, the plating metal supplies metal ions or is maintained by a suitable electrolyte, and reduction deposits the coating. Plating can improve appearance or corrosion resistance. State the electrode roles and the ion that gains electrons.
A simple cell uses two different electrodes in an electrolyte to convert chemical energy to electrical energy. The more reactive metal tends to lose electrons. A hydrogen fuel cell uses hydrogen and oxygen to generate electricity directly, with water as the reaction product. K324 does not require detailed fuel-cell construction.
Formulae and relationships
| Relationship | Use |
|---|---|
| Represent oxidation at an anode. | |
| Represent reduction and metal deposition at a cathode. | |
| Give the overall hydrogen fuel-cell reaction. |
Worked examples
Example 1: Predict the cathode product when aqueous copper(II) sulfate is electrolysed with inert electrodes, and write the half-equation.
- List the cations available in aqueous solution, including copper(II) and hydrogen ions.
- Use selective discharge: copper is deposited rather than hydrogen under the stated conditions.
- Balance charge by adding two electrons to copper(II) ions.
Answer: Copper; .
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Track oxidation and reduction through oxygen, hydrogen, electrons, and oxidation states where appropriate.
- Use reactivity and displacement evidence to identify electron transfer and oxidising or reducing agents.
- For electrolysis, identify mobile ions, electrode products, electron flow, and the effect of concentration or electrode material.
Official outcome coverage
K324 C7: 4 mapped outcomes, references C7(a), C7(b), C7(c), C7(d). Check the official K324 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Record electrode observations and test products safely, keeping the external electron path separate from ion movement in the electrolyte.
Exam traps and retrieval check
Avoid these traps
- Assigning oxidation to the cathode or reduction to the anode.
- Predicting aqueous electrolysis products as if no water-derived ions were present.
- Applying Pure K324 electrolysis detail automatically to Combined Chemistry.
Check from memory
Where does reduction occur in electrolysis?
At the cathode, where cations gain electrons.
What is the object being plated?
The cathode.
What does a simple cell convert?
Chemical energy into electrical energy.
Pure versus Combined scope
Combined Chemistry retains Redox Chemistry but narrows the outcomes. The reviewed Combined component does not include the Pure K324 electrolysis outcomes.
Shared explanation source
Eclat has a related explanation in its existing IP library. It can help with the shared concept, but its IP extensions and school-sensitive scope are not automatically part of K324. Open the related IP explanation.