# Electrolysis

Using electricity to split a molten or dissolved ionic compound into its elements. It is used to extract reactive metals such as aluminium.

Chemistry (school) · Part 07: Metals and electrolysis · Card 7 of 9 · Last updated 2026-10-19

## Analogy

Electricity acts like a crowbar that pulls apart a compound that chemicals alone cannot split.

## Example

**Electrodes**

Cathode (negative): positive ions gain electrons
Anode (positive): negative ions lose electrons

## In practice

Aluminium oxide is split by electrolysis to give aluminium metal and oxygen.

## Practice

### Flashcards

- **Which method extracts metals more reactive than carbon?** Electrolysis.
- **What is the cathode?** The negative electrode, where positive ions gain electrons.

### Interview questions

**Explain why aluminium is extracted by electrolysis but iron can be extracted with carbon.**

- Aluminium is more reactive than carbon
- Carbon cannot displace aluminium from its oxide
- Iron is less reactive than carbon
- Electrolysis needs a lot of electricity so it costs more

**Describe what happens at each electrode in the electrolysis of molten lead bromide.**

- Lead ions move to the cathode and gain electrons
- Lead metal forms at the cathode
- Bromide ions move to the anode and lose electrons
- Bromine gas forms at the anode

## Questions people ask

### Why is electrolysis expensive?

It uses large amounts of electricity. Aluminium production needs a huge current and the compound must be kept molten. To lower costs, aluminium oxide is dissolved in molten cryolite, which melts at a lower temperature than the oxide alone. Recycling aluminium needs only a fraction of that energy.

### What happens when you electrolyse a salt solution?

Water also contributes ions, so the products can differ from a molten salt. In sodium chloride solution, hydrogen forms at the cathode, since it is less reactive than sodium, and chlorine forms at the anode. Sodium hydroxide stays in the solution.

## Related concepts

- [Extraction by carbon](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-7/chemistry-school-part-7-concept-6)
- [Electrolyte](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-7/chemistry-school-part-7-concept-8)
- [Reactivity series](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-7/chemistry-school-part-7-concept-1)
- [Oxidation](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-7/chemistry-school-part-7-concept-3)

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