The Volumes of Hydrated Glucose, Sucrose and Raffinose Molecules, and the Osmotic Pressures of These Aqueous Saccharide Solutions as Measured by the Freezing-Point-Depression Method

Abstract The osmotic pressures of aqueous saccharide solutions were calculated from the data obtained by means of the freezing-point-depression method. Thus, the water activity and the osmotic pressure of d-glucose, sucrose, and raffinose solutions were measured by the freezing-point-depression method. For dilute aqueous saccharide solutions, the freezing-point depression was proportional to their molal concentrations. However, the higher the molal concentration, the larger the freezing-point depression observed became than those to be expected from the molal concentration dependent on the size of the saccharide molecules. The osmotic pressures calculated from the data of the freezing-point-depression method were compared with those measured with semi-permeable membranes by Morse and his colleagues. To obtain the apparent volumes of hydrated d-glucose, sucrose, and raffinose molecules, their partial molal volumes were measured, together with the partial molal volumes of the water of their solutions. The partial molal volumes of the water were verified to be equal to the molar volumes of pure water up to the highest concentrations examined. The apparent volumes of the hydrated d-glucose, sucrose, and raffinose molecules were calculated to be 0.1865, 0.3525, and 0.5105 nm3 respectively.