Strong vs weak acids

Science

Definition

Strong acids completely dissociate into ions in water, meaning every molecule releases a hydrogen ion. Weak acids only partially dissociate, establishing an equilibrium between the undissociated acid and its ions. This distinction affects pH, conductivity, and reactivity.

Examples

  • Hydrochloric acid (HCl) is a strong acid that fully ionizes — stomach acid is mostly HCl
  • Acetic acid (CH₃COOH) in vinegar is a weak acid, only about 1% dissociated in solution
  • Sulfuric acid (H₂SO₄) is a strong acid used in car batteries, while citric acid in lemons is weak
Key Fact

Strong acids (HCl, HBr, HI, HNO₃, H₂SO₄, HClO₄) fully dissociate; weak acids have a Ka value indicating partial dissociation.

Related Terms

Acid-base theory Ph scale Ph calculations Buffers

Study This Concept

Practice strong vs weak acids with free review games in these units:

AP Chemistry Unit 8: Acids and Bases