In aqueous acid-base equilibrium, every acid has a conjugate base and every base has a conjugate acid, and the strength of an acid or base (quantified by its equilibrium ionization constant, K_a or K_b) is inversely related to the strength of its conjugate: a strong acid's conjugate base is ineffective, and vice versa, such that neither member of a conjugate pair can simultaneously be strong. This relationship is formalized by the identity K_a × K_b = K_w (equivalently pK_a + pK_b = pK_w = 14 at 25°C), derived by combining the ionization equilibria of an acid and its conjugate base in water, and it underlies the classification of acid-base problems (strong acid/base, weak acid/base, and buffer systems, including salt hydrolysis as a combination of weak-acid and weak-base cases) within general chemistry's treatment of aqueous equilibrium.
In aqueous acid-base equilibrium, every acid has a conjugate base and every base has a conjugate acid, and the strength of an acid or base (quantified by its equilibrium ionization constant, K_a or K…