A conjugate base is the species formed when a Brønsted acid donates a proton (H⁺). It differs from the original acid by one fewer proton and can itself accept that proton in the reverse reaction. For example, when hydrogen chloride (HCl) donates a proton, its conjugate base is the chloride ion (Cl⁻).

共轭碱是布朗斯特酸给出一个质子(H⁺)后形成的物种。它比原来的酸少一个质子,并能在逆反应中接受该质子。例如,氯化氢(HCl)给出一个质子后,其共轭碱是氯离子(Cl⁻)。