Correlation of activity coefficients of alkyl-ammonium salt solutions

Abstract

An estimation method proposed in a previous paper [St. Perisanu, Rev. Roum. Chim. 46 (2001) 1273–1280], for the activity coefficients of organic electrolytes uses the UNIFAC equation, based on group contributions. The activity coefficient of the solute is expressed as a sum of three terms: (a) electrolytic, considered as equal to the activity coefficient of a solution of same concentration of a salt of the same class not containing any organic radical; (b) non-electrolytic, corresponding to the interactions between organic radicals and solvent molecules and calculated with the UNIFAC theory; and (c) associative, due to association processes of organic ions. The latter term was calculated from experimental values of activity coefficients of organic electrolytes and the first two contributions to their values. It was observed that the associative term is a universal function of a reduced concentration, within a certain class of organic electrolytes. The reference concentration used in order to obtain the reduced values depends on the number of carbon atoms of the molecule. Its value changes only slightly, when the counter ion is changed. The correlation, generated for aqueous solutions was tested also for solutions in organic solvents.