Conjugate acid

Within the Brønsted-Lowry (protonic) theory of acids and bases, a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. A conjugate acid can also be seen as the chemical substance that releases a proton in the backward chemical reaction. Thus, the term acid. The base produced, X⁻, is called the conjugate base and it absorbs a proton in the backward chemical reaction. In aqueous solution, the chemical reaction involved is of the form

HX + H₂O X⁻ + H₃O⁺

This principle is discussed in detail in the article on acid-base reaction theories.

The conjugate base of a weak acid is a strong base, and the conjugate base of a strong acid is a weak base, and vice versa.

Tabulated below are several examples of conjugate acid-base pairs. Acid strength decreases and base strength increases down the table. (The dissociation reaction reaches equilibrium further to the right, with more X⁻ produced.)

See also

• protonation