Tracer diffusion coefficients of I–, I –3, Fe2+ and Fe3+ at low temperatures
Abstract
Tracer diffusion coefficients (Di) have been determined by measuring the limiting oxidation or reduction currents at a large platinum rotating-disc electrode. The systems studied at 5 °C were I–, Fe2+ and Fe3+ in an aqueous supporting medium of 0.05 mol dm–3 HClO4 made up to an ionic strength of 0.1 mol dm–3 with NaClO4, and I–3 in 0.05 mol dm–3 HClO4–0.05 mol dm–3 Nal. The last three ions were also studied at 10, 15 and 20 °C. The resulting activation energies were similar to the value expected from the Stokes–Einstein equation. The values of Diη/T, where η is the viscosity of the solution and T the absolute temperature, have been compared with appropriate literature data at 25 °C. The effective hydrodynamic radii of the four ions have been calculated and interpreted in structural terms.