In a Bronsted-Lowry reaction, a proton (H⁺) is transferred from an acid molecule or ion to a basic molecule or ion. In the process the acid loses one proton (H⁺) to become a base.

The acid and the resultant base are inextricably linked or conjugated. Thus the acid that loses a proton forms a conjugate base. Likewise when the initially basic molecule or ion accepts a proton it forms a conjugate acid. In every Bronsted-Lowry reaction, there are two conjugate acid-base pairs.