ELECTROLYTE DIFFUSION IN MULTICOMPONENT SOLUTIONS

(1) Diffusion in Mixed Electrolyte Solutions. Electrolyte solution theory has been used to study multicomponent diffusion in mixed electrolyte solutions. At low ionic strength precise L(,ik) phenomenological coefficients can be calculated from limiting ionic conductivities and the solvent properties. If activity coefficients for the dilute mixed electrolytes are available, precise multicomponent diffusion coefficients can also be calculated. Explicit equations are given for calculating both sets of transport coefficients. Differences in ionic mobilities lead to electrostatic coupling between diffusive flows of electrolytes. Ternary diffusion is examined in detail for a few aqueous systems. Strongly coupled diffusion and highly variable diffusion coefficients may be anticipated for aqueous systems containing acids or hydroxides. A modified Harned conductimetric experiment for the determination of ternary diffusion coefficients is described. Results for the system hydrochloric acid/potassium chloride/water (25(DEGREES)C) are in good agreement with theory.; (2) Electrolyte Diffusion in Mixed Solvents. Diffusion coefficients have been measured conductimetrically at 25(DEGREES)C for dilute electrolytes in the following systems: potassium chloride/methanol (40% by weight)/water; hydrochloric acid/methanol(10, 20 and 40%)/water; and potassium chloride/t-butanol (9.54 and 17.80%)/water. The results are correctly described by theory based on pseudo-binary electrolyte diffusion. Ion association and departures from pseudo-binary behavior are considered as possible sources of error. Electrolyte activity coefficients were derived from the diffusion data. The activity coefficients for hydrochloric acid agree very well with precise emf results.; (3) Mixed Electrolyte Diffusion in Mixed Solvents. Diffusion coefficients for dilute hydrochloric acid/potassium chloride have been mesured at 25(DEGREES) in a mixed solvent of water and methanol (10% by weight). The experimental diffusion coefficients and the derived L(,ik) phenomenological coefficients are in excellent agreement with predictions based on pseudo-ternary mixed electrolyte diffusion theory. The results suggest that reliable electrolyte diffusion properties can be predicted from limiting ionic mobilities for any arbitrary ionic mixture at low ionic strength in any arbitrary solvent, as long as the dielectric constant is high enough to give effectively total dissociation. Strong coupling between diffusive flows of electrolytes may be anticipated in aqueous mixed solvents containing acids.