a b s t r a c tExperimental values for mutual diffusion coefficients (interdiffusion coefficients) for CaCl 2 aqueous solutions at 298.15 K and 310.15 K, not available in the literature, were experimentally determined between 0.005 mol dm −3 and 0.1 mol dm −3 . The measurements were performed by using a conductimetric openended capillary cell. Values at infinitesimal concentration, D 0 , were also obtained. These data were analysed using the Onsager-Fuoss and Gordon models. In addition, molar conductance data were measured at 310.15 K for CaCl 2 aqueous solutions at the same concentration range and the value at infinitesimal concentration determined. Afterwards, it was split into the ionic limiting values. By replacing them into the Nernst equation, diffusion coefficients at infinitesimal concentration were derived (1.335 × 10 −9 m 2 s −1 and 1.659 × 10 −9 m 2 s −1 ) at both temperatures (298.15 K and 310.15 K, respectively). They agree well with the extrapolated experimental ones (1.312 × 10 −9 m 2 s −1 and 1.613 × 10 −9 m 2 s −1 ).

Numerical values for the mean distance of closest approach of ions, "a", for lithium salts in aqueous solutions are presented and discussed. These values were obtained from both experimental activity and diffusion coefficients, and estimated by using different theoretical approaches.