根据酸碱质子理论，一分子或离子 X （以负一价离子为例）的共轭酸是该分子或离子得到一个质子后的产物 HX，而 X 则为 HX 的共轭碱，X和 HX 组成一组共轭酸碱对。以下是水溶液中，X的共轭酸 HX 和水的反应平衡式

一强碱的共轭酸会是弱酸，而一弱碱的共轭酸会是强酸。

总而言之，这可以被表示为下面的化学反应：

常见的共轭酸碱对有：

A conjugate acid, within the Brønsted–Lowry acid–base theory, is a species formed by the reception of a proton (H) by a base—in other words, it is a base with a hydrogen ion added to it. On the other hand, a conjugate base is merely what is left after an acid has donated a proton in a chemical reaction. Hence, a conjugate base is a species formed by the removal of a proton from an acid.