The calculation of ion pair diffusion coefficients: A comment |
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| Authors: | Kenneth S Johnson |
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| Institution: | Marine Science Institute, University of California, Santa Barbara, CA 93106 U.S.A. |
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| Abstract: | It is shown that the values of the diffusion coefficient of MgSO40 ion pairs computed by Harned and Hudson (J. Am. Chem. Soc., 73: 5880, 1951) and Katz and Ben-Yaakov (Mar. Chem., 8: 263, 1980) are too high by a factor of 2. The correct value of the ion pair diffusion coefficient at infinite dilution was obtained from the measured mutual diffusion coefficient after applying corrections for incomplete dissociation, the electrophoretic effect, the viscosity of the solution and the effect of chloride ion pairs (in the ionic media used during measurements of the stoichiometric association constant of MgSO40 ion pairs). The MgSO40 diffusion coefficient is calculated to be 0.65 × 10?5 cm28?1. The result is independent of the concentration up to a value of 0.8 mol dm?3.Values were also calculated for the diffusion coefficients of the following ion pairs: NaSO4? (0.81 × 10?5), CaCl+ (0.78 × 10?5), BaCl+ (0.85 × 10?5), NaCl0 (0.86 × 10?5), KCl0 (1.09 × 10?5), NH4Cl0 (1.10 × 10?5) and CaCl0 (1.27 × 10?5). In general, the diffusion coefficients are less than those of the free ions. The results show quantitative agreement with theoretical predictions. |
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