Redox, Electrolysis and Cells — Where Electrons Actually Go

A car battery, a rusting gate, a silver-plated spoon and an aluminium smelter are the same chemistry four times over. In each, electrons leave one substance and arrive at another.

That transfer has two halves and they are inseparable. Oxidation is loss of electrons; reduction is gain. Neither happens alone, which is why the pair is called a redox reaction.

Once you see a reaction as electron traffic, two questions answer everything: who lost electrons, and who took them. The loser has been oxidised and is the reducing agent. The taker has been reduced and is the oxidising agent.

That last sentence is where most marks are won or lost, because it feels backwards. The oxidising agent oxidises something else, and in doing so it is itself reduced. Say it aloud until it stops sounding wrong.

Everything else in this topic — cells, electrolysis, corrosion — is that one idea in different equipment.

1. In any electrochemical cell, reduction always takes place at the

2. While electroplating a steel spoon with silver, the spoon must be connected as the

3. In a redox reaction, the oxidising agent is the species that

4. In the electrolysis of brine (the chlor-alkali process), the gas liberated at the anode is

5. In a Daniell cell, which electrode is the negative terminal and gradually loses mass?

6. The electrolyte used in a lead storage battery is

7. Galvanisation protects iron by coating it with a layer of

8. What is the oxidation number of sulphur in H₂SO₄?