Brønsted–Lowry Acid–Base Equilibria in Aqueous Solution (Oxford AQA International A Level Chemistry): Revision Note

Brønsted–Lowry Acid & Bases

• The Brønsted-Lowry Theory defines acids and bases in terms of proton transfer between chemical compounds

• A Brønsted acid is a species that can donate a proton

  • For example, hydrogen chloride (HCl) is a Brønsted acid as it can lose a proton to form a hydrogen (H⁺) and chloride (Cl^-) ion

            HCl (aq) → H⁺ (aq) + Cl^- (aq)

• A Brønsted base is a species that can accept a proton

  • For example, a hydroxide (OH^-) ion is a Brønsted base as it can accept a proton to form water

OH^- (aq) + H⁺ (aq) → H₂O (l)

The Brønsted-Lowry Base behaviour of water and ammonia

Acid-base equilibria

• The Brønsted-Lowry Theory is not limited to aqueous solutions only and can also be applied to reactions that occur in the gas phase

A Brønsted-Lowry acid and base reaction