Applicability of Fuoss's Conductance Equation to Dilute Electrolytic Solutions in Aqueous, Nonaqueous, and Aquo‐Organic Mixtures

Abstract

The concentration dependence data of electrical conductances for dilute solutions of , , , , ,, , and in water ; and in 50 mol percent mixtures ; , ,, , , and in ; , , and in ; and in ; tetra‐n‐propyl‐ and tetra‐n‐butylammonium bromides and iodides (, , , and ) in ; and , , , , and in dioxane‐water mixtures (in the dielectric ranges ,, , , and , respectively) at 25°C have been analyzed using the Fuoss‐Onsager‐Skinner (FOS‐65) and Fuoss‐1978 (F‐78) conductance equations. The parameters of the former equation are found to differ significantly from those of the latter. The deviation in the limiting equivalent conductance is less than 0.001% in the F‐78 treatment of data as compared to ∼0.01–0.6% in the FOS‐65 treatment. The value of ionic association constant for a given salt is found to depend on the model by which the data have been analyzed. Unlike the prediction of FOS‐65, the usual exponential dependence of on dielectric constant shows curvature, which can be attributed to the two‐step association mechanism demanded by F‐78. The values of ion‐size parameter aå of FOS‐65 are low in comparison with the Bjerrum distance parameter and vary erratically with , while those of the cosphere diameter of F‐78 show a consistent trend of behavior. In view of these results, the FOS‐65 treatment does not seem to be generally applicable.