INTRADIFFUSION COEFFICIENTS FOR PERCHLORATE IONS IN ZINC PERCHLORATE AND ZINC-CHLORIDE SOLUTIONS AT 25-DEGREES-C - COMPARING TRANSPORT-PROPERTIES OF ZINC-CHLORIDE AND ZINC PERCHLORATE SYSTEMS

Intradiffusion coefficients for (ClO4-)-Cl-36 have been measured in so lutions of zinc perchlorate of concentration 0.1 to 3 mol dm(-3) at 25 degrees C by the diaphragm cell technique. In addition, intradiffusio n coefficients for perchlorate ions in zinc chloride solutions have be en measured over a concentration range at 25 degrees C. The results co nfirm previous work on the effect of complexation on diffusion in zinc chloride solutions above a salt concentration of 0.1 M. The present d ata, together with literature data for diffusion coefficients of the o ther species present in the zinc perchlorate electrolyte system, have enabled a simple analysis of the hydration around the zinc ions to be carried out. This indicates that the water diffusion data are consiste nt with the zinc ions having an effective hydration sphere of 11 (+/-2 ) water molecules. This is in keeping with values obtained for other s imple divalent electrolytes using the same model. The model is extende d here to allow analysis of water diffusion in zinc chloride solutions taking into account the presence of complexed chloro-zinc species. Th e experimental data are consistent with the effective hydration of the chloro-zinc complexes being independent of the number of chloride lig ands and equal to 18+/-3 over a concentration range of 0 tol mol-dm(-3 ). This postulate is discussed in terms of its consequences on the wat er ligand dynamics for the complex equilibria.