Apparent molar volumes of alkaline earth hexacyanocobaltates (III) in aqueous solution at 25°C

The apparent molar volumes of Mg, Ca, Sr, and Ba hexacyanocobaltates (III) have been determined from 1×10⁴ to 0.2M (mol-dm^–3), using both vibrating tube densimeter and dilatometric methods. The semiempirical Pitzer equation has been used to reproduce the experimental data. Positive deviations from the Debye-Hueckel limiting law (DHLL) have been observed at C<0.01M and are compared with the predictions of two other electrostatic approaches, the DHLL+B₂ approximation of the Mayer theory and the numerical integration of the exponential Poisson-Boltzmann equation. A least squares procedure has been used to obtain the best fit parameters, including the apparent molar volume at infinite dilution.