Definition: A conjugate acid-base pair consists of two species that transform into each other by the gain or loss of a proton.

Formation: When an acid donates a proton, it forms its conjugate base; when a base accepts a proton, it forms its conjugate acid.

Example Reaction:

HA+H2O⇌A−+H3O+

HA (acid) loses a proton to become A⁻ (conjugate base).

H₂O (base) gains a proton to become H₃O⁺ (conjugate acid).

Note: The conjugate base is always one proton (H⁺) less than its acid; the conjugate acid is always one proton more than its base.

Relative Strength of Acids and Bases

• Strong Acids and Bases: Completely dissociate in water. Their conjugate counterparts are weak.

• Weak Acids and Bases: Partially dissociate in water. Their conjugate counterparts are relatively stronger.

Examples of Common Conjugate Pairs

• Acetic Acid and Acetate Ion: Acetic acid (CH₃COOH) is a weak acid, and acetate ion (CH₃COO⁻) is its conjugate base.

• Ammonia and Ammonium Ion: Ammonia (NH₃) is a weak base, and ammonium ion (NH₄⁺) is its conjugate acid.