Conjugate acid

In 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. The base produced, X^-, is called the conjugate base. 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.

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.)