DISSOCIATION-CONSTANT OF A WEAK ELECTROLYTE IN CHARGED MEMBRANE

In this study, the dissociation constant of acetic acid as a weak elec trolyte in an ion-exchange membrane, (K) over bar, was estimated using the Donnan equilibrium theory, which has been applied to a strong pol yelectrolyte membrane. The membrane charge density and the total conce ntration, which represents the sum of the dissociated proton concentra tion and carboxyl concentration of the undissociated electrolyte in th e membrane, were determined by neutral titration; the charge effective ness was determined from membrane potential measurements; and the prot on concentration in the external solution phase was determined by Donn an equilibrium theory and used for the calculation of (K) over bar. Th e dissociation constants, (K) over bar, in the cation exchange membran e were on the order of 10(-4) and were larger than that in water (= 1. 73 x 10(-5)). The value of (K) over bar increased with an increase in the concentration in the external solution and decreased with the fixe d charge density increase. It is suggested that the fixed charge group depresses the dissociation of the weak electrolyte.