A New Look on the Representation of Electrical Conductivities in Mixed Solvents. The Universal Curves of Limiting Conductances of Electrolytes and the Modified and the Excess Walden Products

Concepts of the modified and the excess Walden products are introduced and discussed when applied together with the ordinary Walden product. The existence of the universal curves of limiting conductances for electrolytes (or for ions) in a given pair of solvents are further examined for a number of mixtures which include ethanol, 2-propanol, 1,1,1,3,3,3hexafluoro-2-propanol, N,N,-dimethylformamide and 1,4-dioxane with acetone; methanol, 1,4-dioxane, carbon tetrachloride and toluene with acetonitrile; water, methanol and γ-butyrolactane with tetramethylene sulfone; methanol, acetonitrile, toluene, dimethoxymethane and dimethoxyethane with propylene carbonate. Many electrolytes were involved in the evaluation of the universal curves, but the majority are alkali metal halides and tetraalkylammonium salts. These universal curves allow to estimate values of limiting conductances of electrolytes and give an indication about the quality of the performed conductivity measurements. The existence of universal curves of limiting conductances indicates that the properties of electrolytes in pure solvents are, to a great extent, preserved also in the mixture of solvents due to the simple dilution effect. In some cases, for a limited concentration range, it was observed that for a given electrolyte, the limiting conductances are weakly dependent on the type of the second component in the mixture, e.g. in waterrich–alcohol mixtures. A formal mathematical representation of the universal curves (two-adjustable parameter equation) and the limiting conductances (three-adjustable parameter equation) are introduced and for many electrolytes in numerous mixed-solvent systems these parameters are reported.