Self-Complexing and Transport Processes in Aqueous Solutions of Group IIb Metal Halides

Potentiometric measurements on aqueous solutions of zinc chloride have been made in the concentration range 0.0004 - 1.0 mol. kg-1. The standard electrode potential of zinc electrode in zinc chloride and the activity coefficients for this salt have been calculated, taking into account incomplete dissociation. Comparison with literature data has been made and reasons for discrepancies are suggested. Existing potentiometric data on aqueous cadmium iodide has been used to obtain refined values of stability constants and concentrations of Cdlx 2-x (x=1,2,3,4) complexes by the relatively new method, reported by Reilly and Stokes in 1970. It is shown that this method can be used with a fair degree of confidence for heavily complexed systems such as cadmium iodide and cadmium chloride. For salts which are complexed to a lesser degree, the method may lead to dubious results mainly because of computational difficulties. This has been assessed in the light of results obtained for zinc chloride. The theory of irreversible thermodynamics has been applied to transport processes in aqueous cadmium iodide solutions. Relations are derived, in terms of phenomenological coefficients, which lead to the prediction of experimentally measurable quantities, transport number, equivalent conductance and salt diffusion coefficients. The analysis has been further extended to include isotopic-diffusion of cadmium ion in cadmium iodide solutions. The predicted transport parameters are compared with those derived from experimental measurements. The isotopic-diffusion of cadmium in cadmium iodide has been studied by the diaphragm-cell method. A new type of diaphragm cell magnetic stirring unit capable of accommodating four diffusion cells has been designed and constructed. Its advantages over the previous systems are discussed. Several computer programs have been written for involved and repetitive calculations