# Strong and weak acids

A strong acid fully splits into ions in water. A weak acid only partly splits. Strength is different from concentration.

Chemistry (school) · Part 06: Acids, bases and salts · Card 7 of 9 · Last updated 2026-10-19

## Analogy

A strong acid is a bag of sweets that is all handed out. A weak acid hands out only a few.

## In practice

Hydrochloric acid is strong. Ethanoic acid, found in vinegar, is weak.

## Practice

### Flashcards

- **What is the difference between a strong and a weak acid?** A strong acid splits fully into ions. A weak acid only partly splits.

### Interview questions

**Explain the difference between a strong acid and a concentrated acid.**

- Strong means fully ionised in water
- Concentrated means lots of acid per unit of volume
- A weak acid can be concentrated
- A strong acid can be dilute

## Questions people ask

### Is a strong acid always more dangerous than a weak one?

Not always. Hazard depends on strength and concentration. A very concentrated weak acid can be harmful, while a very dilute strong acid may be fairly safe. Hydrochloric acid at the same concentration as ethanoic acid reacts faster because it has more free hydrogen ions.

### How can you tell a strong from a weak acid in an experiment?

Compare solutions of the same concentration. The strong acid has a lower pH, reacts faster with magnesium and conducts electricity better, since it has more free ions. The weak acid has a pH closer to 7, such as 3 rather than 1.

## Related concepts

- [Acid](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-6/chemistry-school-part-6-concept-1)

Web page: https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-6/chemistry-school-part-6-concept-7
Study this card in the app: https://studyvisually.com/app/learn?category=chemistry-school&card=chemistry-school-part-6-concept-7