Ternary diffusion with charged-complex formation in aqueous I2+NaI and I2+KI solutions

Abstract

Diaphragm cells have been used to measure ternary diffusion coefficients for I2+NaI and I2+KI in aqueous solution at 25°C. Although most of the iodine molecules are bound to iodide ions and are transported as the triiodide species [I2(aq)+I−(aq)=I 3 − (aq)], diffusion of the iodide salts produces relatively small countercurrent coupled flows of the iodine component. The ternary diffusivity of the iodine component in the solutions is 10 to 20% larger than the diffusivity of the triiodide species. This behavior can be understood by considering electrostatic coupling of the ionic flows. The diffusion equations for I2+NaI and I2+KI components are reformulated in terns of NaI3+NaI and KI3+KI mixed electrolyte components.