Thermodynamics of aqueous solutions of the alkali metal sulfates

The available thermodynamic properties for aqueous solutions of each of the alkali metal sulfates have been combined and analyzed within the framework of the ion interaction model at temperatures up to 225/sup 0/C. It was necessary to set ..cap alpha../sub 1/ equal to 1.4 kg /SUP 1/2/ -mol /SUP 1/2/ in order to obtain a satisfactory fit. The temperature dependence of the ion interaction parameters was given the functional form used by Rogers and Pitzer in their study of Na/sub 2/SO/sub 4/(aq). With few exceptions, it was possible to reproduce the available thermodynamic data for aqueous solutions of the alkali metal to within the estimated experimental error. Thermodynamic results for Na/sub 2/SO/sub 4/(aq) appear to be adequate in this temperature range, but enthalpy and heat capacity data for the other alkali metal sulfate solutions are conspicuously lacking. Activity coefficients of these electrolytes decreased to less than 0.1 at moderate molalities at the higher temperatures, and their order changed with increasing temperature; two results which could be due to a combination of hydration and association effects.