What constitutes a conjugate acid-base pair?

A conjugate acid-base pair consists of two species that differ by the presence or absence of a proton (H⁺). When an acid donates a proton, it forms its conjugate base, while the conjugate acid is formed when a base gains a proton. This relationship is fundamental in the Brønsted-Lowry theory of acids and bases, which describes acids as proton donors and bases as proton acceptors.

For example, when acetic acid (CH₃COOH) donates a proton, it becomes acetate ion (CH₃COO⁻), which is its conjugate base. Conversely, if the acetate ion accepts a proton, it reforms acetic acid. This proton transfer between the acid and its conjugate base defines the nature of the conjugate acid-base pair, making this concept essential for understanding acid-base chemistry.