Self-diffusion of Co 2+ ions in CoCl 2 and CoSO 4, and electrolyte-diffusion of CoSO 4 and ZnSO 4 in agar gel medium

Abstract

Self-diffusion of Co 2+ ions in CoCl 2 and CoSO 4 in the concentration range of 10 −5 to 0.25 M is studied in 1% agar gel at 25°C using zone-diffusion technique. The divergence observed between theoretical and experimental values of diffusion coefficients in both systems is explained on the basis of various types of interactions occurring in the system. The applicability of the transition state theory to the diffusion of ZnSO 4 in agar gel medium is tested by varying the temperature of the system as well as the gel concentration. The activation energy and D 0 value decrease with increasing gel concentration, in agreement with the theory. The obstruction effect determined in terms of α-value, describing the relative lowering of the diffusion coefficient in gel medium in comparison with the pure solution, in the diffusion of ZnSO 4 is found to be independent of temperature. The effect of electrolyte concentration on obstruction effect and on activation energy ( E) for diffusion of CoSO 4 is also examined. The decrease in α and E values with electrolyte concentration is explained by considering the competitive hydration between ions and agar molecules and Wang's model respectively.