An Approach to the Problem of the Dependence of the Dissociation Constant of Weak Electrolytes on the Temperature and the Solvent Composition in the Ethane-1,2-diol / 2-Methoxyethanol Solvent System.

This empirical approach to clarify the problem of the dependence of the dissociation constants of weak electrolytes on temperature and composition of mixed solvents systems (X) is applied to the dissociation constant of picric acid in ethane-1,2-diol, in 2-methoxyethanol and in their binary mixtures. The data utilized here are those of previous work (recalculated by means of the more accurate Fuoss–Hsia equation) integrated by the experimental data relative to three new mixtures. Two equations of the dependence of K on T and of K on X, respectively, are suggested and good accordance between experimental and calculated values is shown. Starting from the two above-mentioned equations, general empirical equations for the surface K(T, X) are proposed; the average difference between calculated and experimental K values is ca. 8 %. A three-dimensional plot of the function K=K(T, X) is presented. The proposed empirical models are compared to that obtained for the previously studied ethane-1,2-diol–water solvent system and advantages and limitations of the models are discussed.