Mutual diffusion coefficients of SrCl2–H2O and CsCl—H2O at 25 °C from Rayleigh interferometry

Abstract

The volume-fixed mutual diffusion coefficients of SrCl₂–H₂O and CsCl–H₂O have been measured from dilute solution to near saturation to an accuracy of 0.1–0.2% at 25 °C, using free-diffusion Rayleigh interferometry. A few diffusion coefficients were also measured for NaCl—H₂O, as were the densities of SrCl₂–H₂O. These new data are compared with other available diffusion and density data for these salts. Diffusion coefficients are now available for most of the aqueous alkali-metal and alkaline-earth chlorides. The effects of cation size and ionic hydration on diffusion coefficients are discussed for these two series. The mutual diffusion coefficients of the alkaline-earth chlorides have crossovers as a function of the molarity, as do those of 2–2 sulphates. In contrast, their thermodynamic diffusion coefficients not only have no crossovers, but reduce the differences between weak and strong electrolytes.