# Brønsted-Lowry acids and bases

A Brønsted-Lowry acid gives away a proton (H⁺). A base accepts one. When an acid loses a proton, it becomes its conjugate base. When a base gains one, it becomes its conjugate acid.

Chemistry (university) · Part 08: Acids, bases and electrochemistry · Card 1 of 9 · Last updated 2026-10-19

## Analogy

Passing a ball in a game: the acid throws the proton, the base catches it, and now each holds the other's role.

## Example

**HCl + H₂O ⇌ Cl⁻ + H₃O⁺**

HCl: acid
H₂O: base
Cl⁻: conjugate base of HCl
H₃O⁺: conjugate acid of H₂O

## In practice

In a cup of lemon juice, citric acid passes protons to water molecules, making H₃O⁺ that tastes sour.

## Practice

### Flashcards

- **What is a Brønsted-Lowry acid?** A proton (H⁺) donor.

## Questions people ask

### What makes an acid strong?

A strong acid ionizes almost completely in water, so nearly every molecule gives up its proton. HCl, HBr, HI, HNO₃, H₂SO₄ and HClO₄ are the common examples. The stronger the acid, the weaker its conjugate base, because a weak base holds on poorly to the proton it just lost.

### What is an amphoteric substance?

An amphoteric substance can act as an acid or a base depending on what it meets. Water is the classic example: it gives a proton to ammonia and accepts a proton from HCl. Species like HCO₃⁻ and H₂PO₄⁻ also behave this way.

## Related concepts

- [pH and Kw](https://studyvisually.com/learn/science/chemistry-university/chemistry-university-part-8/chemistry-university-part-8-concept-2)
- [Weak acids and Ka](https://studyvisually.com/learn/science/chemistry-university/chemistry-university-part-8/chemistry-university-part-8-concept-3)

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