Cambridge O Level Chemistry · Syllabus 5070 · Acids, Bases and Salts
Weak Acid
What is Weak Acid?
An acid that is only partially dissociated into ions in aqueous solution, so that most of the acid remains as un-ionised molecules at any moment. Carboxylic acids such as ethanoic acid are weak acids, and their dissociation is written with an equilibrium arrow.
This definition is part of the Acids, Bases and Salts chapter in Cambridge O Level Chemistry.
Common mistakes with Weak Acid
- “A strong acid is a concentrated acid, or a corrosive one.” Repair Strong describes the extent of dissociation in aqueous solution: complete for a strong acid, partial for a weak one. Concentrated describes how much acid there is per unit volume. They are independent, so a dilute strong acid and a concentrated weak acid both exist.
Questions students ask about Weak Acid
What is the difference between a strong acid and a concentrated acid?
Strong describes how completely the acid dissociates into ions in solution: a strong acid dissociates completely, a weak acid only partially. Concentrated describes how much acid is dissolved per unit volume. The two are independent, so a dilute strong acid and a concentrated weak acid can both exist — hydrochloric, nitric and sulfuric are the strong acids on this syllabus, and ethanoic acid is weak.