Activity Coefficients of Aqueous Xylose and Maltose Solutions

Osmotic and activity coefficients of aqueous xylose and maltose solutions at 25°C are measured by the isopiestic vapor pressure method. Densities of these solutions are also determined at 25°C. The activity coefficients of water in these solutions show that both xylose and maltose solutions do not behave as regular solutions. Second virial coefficients for xylose and maltose are calculated from partial molar volumes of the solute and the solvent at infinite dilution and empirical equations of water activity coefficient. The coefficients calculated for xylose and maltose are 111 and 248 cc/mol, respectively. Second virial coefficients for these sugars and a few other sugars are approximately proportional to the molecular weight. This relation is explained by the van der Waals model.