The MC activity coefficient function for acid–base equilibria. Part I. New methods for estimating pka values for weak bases

Abstract

An experimental linear relation in strong aqueous acids between overlapping indicators, available for the whole acidity range, allows the determination of the pK_a values of weak bases by a new method of approximation. A new activity coefficient function (M_C) in aqueous sulphuric and perchloric acid is also proposed. The thermodynamic equilibrium constants of various groups of compounds including primary nitroanilines, tertiary amines, amides, indoles, alkoxy- and hydroxy-benzenes, triphenylmethyl alcohols, and sulphoxides, have been reinvestigated and the results compared with those reported in the literature. The solvation effects of the medium on the M_C function are also discussed.