Influence of ionic association on the B coefficient of the Jones–Dole equation for Kl and KCl in water–t-butyl alcohol mixtures at 26°C

Abstract

Viscosity, density and conductivity measurements for KI and KCl solutions in the water–t-butyl alcohol system at 26°C have been performed up to 70 and 50 mol % of alcohol. The values of the A and B coefficients of the Jones–Dole equation are calculated. The limiting molar and ionic conductivities, necessary for calculations of the theoretical A coefficients, are obtained. Both electrolytes turned out to be associated in solutions containing more than 20 mol % of t-butyl alcohol. Thus, ionic association was taken into consideration in calculations of B_i and B_p coefficients, referring to the ion–solvent and ion-pair–solvent interactions, respectively. The experimental criterion B_Cl–=B_K+=½B_KCl was applied in order to obtain the ionic B coefficients. In the water-rich region they decrease with the size of ions as they do in water. When the alcohol content increases the ionic B coefficients for anions and cations approach one another and in the case of cations even change their order at ca. 47 mol % of t-butyl alcohol. The last observation could be explained by considering the ionic association which permits the separation of the ion–solvent and ion-pair–solvent interactions.