Tracer diffusion coefficients of I–, I–3, Fe2+and Fe3+at low temperatures

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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.