PH a pH of 7.3. This is clearly wrong as an acid solution should have a pH of less than 7. Treating the system as a mixture of hydrochloric acid and the amphoteric substance water, a pH of 6.89 results. A weak acid or the conjugate acid of a weak base can be treated using the same formalism. First, an acid dissociation constant is defined as follows. Electrical charges are omitted from subsequent equations for the sake of generality and its value is assumed to have been determined by experiment. This being so, there are three unknown concentrations, [HA], [H] and
Acid dissociation constant the added complication that the neutral molecule is subject to an internal acid–base equilibrium in which the basic amino group attracts and binds the proton from the acidic carboxyl group, forming a zwitterion. At pH less than about 5 both the carboxylate group and the amino group are protonated. As pH increases the acid dissociates according to At high pH a second dissociation may take place. Thus the zwitterion, , is amphoteric because it may either be protonated or deprotonated. The equilibrium constant "K" for a base is usually defined as the "association" constant for protonation of the base, B,