The Differential Diffusion Constant of Calcium Chloride in Aqueous Solution

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Abstract
The differential diffusion constant for calcium chloride in aqueous solution has been measured for concentrations ranging from 0.0025 to 0.5 mole per liter and for temperatures from 15° to 35°C. The relation connecting the diffusion constant at a finite concentration with that at infinite dilution, k=k0(1+c∂ ln f/∂c)(η0/η), which holds for moderate concentrations for several 1 — 1 electrolytes, is valid for this salt only up to 0.01 mole per liter; the corresponding value of k0 is about 1.5 percent less than that computed from the ionic mobilities by the Nernst relation. The activation energy of diffusion for a given concentration decreases with rising temperature as is customary; for a given temperature, however, it decreases with increasing concentration in dilute solutions, and finally becomes independent of concentration.