THERMODYNAMICS OF 1-1 ELECTROLYTE MIXTURES IN AQUO-1,4-DIOXANE SOLVENT SYSTEM - MOLAR EXCESS ENTHALPY

Molar excess enthalpy data at 308.15 K for 1 M binary solutions of MX + NY (or NX), MY + NX (or NY), M(or N)X + M(or N)Y (where M is Na+, N is K+, X is Cl-, Y is Br-) electrolytes in 1,4-dioxane (D) + water (x( D) = 0.0142, dielectric constant 70 at 308.15 K) solvent (S) system ha ve been determined using an LKB flow microcalorimeter. The data, which differ appreciably from the corresponding data in water and which dep end, unlike those in water, on the nature of the common cation and com mon anion, do not support Young's cross square rule; this failure has been attributed to the dependence of the hydration of the ions of the MX + NX or MX + NY, etc., 1:1 electrolyte mixtures in S on the nature of (i) the common cation and common anion and (ii) the mixture of anio ns and of cations. The H(E) data of the present systems have been attr ibuted to both the coulombic interactions and the asymmetric effects, and this has been substantiated by an analysis of the data in terms of Friedman's cluster theory. The importance of the virial theory of Pit zer in the determination of the relative magnitudes of the coulombic a nd asymmetric interactions on H(E) data, is also highlighted.