Velocity correlations in aqueous electrolyte solutions from diffusion, conductance and transference data. Application to concentrated solutions of cadmium iodide

Tracer-diffusion and intradiffusion coefficients have been measured for the Cd and Cl ion constituents and for water molecules in aqueous solutions of cadmium chloride in the concentration range 0.1–5.8 mol dm–3 at 298.15 K. These measured coefficients have been combined with transport data from other sources to calculate velocity cross-correlation coefficients (VCCs). In contrast to a fully dissociated 1 : 2 salt such as magnesium chloride, the VCCs for CdCl2 show much greater positivity, and in particular the anion–anion VCC is positive over the whole concentration range. An explanation for the negative transference numbers in concentrated CdCl2 solutions is offered using the linear-response-theory formalism.