Diffusivity of Zinc Ions in Aqueous Alkali-Metal Chlorides

The tracer-diffusion coefficients of radioactive zinc ions in aqueous potassium chloride, cesium chloride, and lithium chloride solutions of concentration between 0.005 and 2.5 mol dm -3 are determined using an open-ended capillary technique with stirring. The theoretical tracer-diffusion coefficients of zinc ions in aqueous salt solutions are calculated using the Gosting-Harned equation and compared with the experimentally determined diffusion coefficients. The measured values of tracer-diffusion coefficients of zinc ions in the aqueous alkali-metal chloride solutions agree with the theoretically predicted values up to a concentration of about 0.05 mol dm -3 . At higher concentrations, the tracer-diffusion coefficient of zinc ions first increases and again decreases with concentration, giving rise to a maximum in the plot of the tracer-diffusion coefficient against the square root of the concentration. A qualitative explanation of the concentration dependence of the tracer-diffusion coefficient of zinc ions in concentrated solutions of the salts is attempted by taking into account the ion-ion and ion-water interactions