CONJUGATE ACIDS AND BASES
Every acid produces, a conjugate base and every base produces a conjugate acid, together forming a conjugate acid base pair. Conjugate means in pair.
Conjugate acid:
A specie formed by accepting a proton by a base.
Conjugate base:
A specie formed by donating a proton by an acid.
Explanation:
Forward and reverse reaction in acid-base equilibrium involves the proton transfer. Consider the following example
In the forward reaction, the CH3COOH donates a proton to H2O. Therefore CH3COOH is a Bronsted-Lowry acid and H2O is a Bronsted-Lowry base. In the reverse reaction CH3COO- accepts a proton from H3O+. Therefore CH3COO- is a base and H3O+ is an acid according to the Bronsted-Lowry concept.
Conjugate Acid-Base Pair:
An acid-base reaction consists of two species acid and base, they differ only by the loss or gain of a proton. The acid in such a pair is called conjugate acid of the base and the base in such a pair is called the conjugate base of the acid.
In the above example,
CH3COO- is a conjugate base of CH3COOH acid.
H3O+ is the conjugate acid of the H2O base.
NOTE:
- A weak acid has a strong conjugate base.
- A weak base has a strong conjugate acid.
- A strong acid has a strong conjugate base.
- A strong base has a weak conjugate acid.