The Apparent Molal Volume and Adiabatic Compressibility of Some Organic Solutes in Water at 25 °C

The apparent molal volumes and adiabatic compressibilities of aqueous solutions of some ureas, thioureas, acetamlde, thioacetamide, dioxane, sugars, and succinic acid have been determined at 25 °C from precise density and sound measurements. The sugars have large negative values for the infinite dilution partial molal adiabatic compressibilities, °~ -16.2 (± 3.3)×10-4 cm-3 mol-1 bar-1 (of the same order of magnitude as amino acids) suggesting that these molecules are highly hydrated. Positive values of ° ~ 7.0 (± 2.6)×10-4 cm-3 mol-1 bar-1 are observed for dioxane, acetamide, thioacetamlde, tetramethylurea, and succinic acid suggesting very little hydration for these molecules in water. For urea, 1, 3-dimethylurea, and thiourea °~ -1.9 (± 1.5)×10-4 cm-3 mol-1 bar-1 suggesting these molecules are slightly hydrated. The degree of hydration increases with the number of functional groups which can hydrogen bond with water molecules. The substitution of sulfur for oxygen causes a decrease In hydration.