Activities of water and solutes in the solution system H2SO4−Cr2(SO4)3−H2O

Abstract

The activities of water in the solution systems of Cr2(SO4)3−H2O and H2SO4−Cr2(SO4)3−H2O were determined at 298 K by an isopiestic method. Properties of the green and violet isomers of Cr2(SO4)3 were considered separately. The activities of water in aqueous solutions containing violet Cr2(SO4)3 alone are considerably smaller than those of the green isomer. The water activities of aqueous H2SO4 solutions containing the violet isomer of Cr2(SO4)3 satisfactorily obey the Zdanovskii rule, while those of the green isomer show an upward deviation from the Zdanovskii linearity. The activities of water in these solution systems were also calculated, using the Robinson-Bower empirical equation, and showed satisfactory agreement with the calculated values, whether the formation of the sulfato-complex, CrSO 4 + , and the dissociation of H2SO4 were taken into consideration or not. The mean activity coefficients of H2SO4 and Cr2(SO4)3, for the solution systems studied in this work, were calculated by applying the McKay-Perring method and its modified form, using the measured water activity data of these solution systems. The concentration dependencies of the mean activity coefficients of H2SO4 and Cr2(SO4)3 in the solutions containing the green isomer are quite different from those of the violet isomer. Particularly, it was found that the activity values of water and solutes in the solution system of H2SO4-violet Cr2(SO4)3−H2O are similar to those of the solution system of H2SO4−Fe2(SO4)3−H2O.