H2O-D2O solvent isotope effect on excess molar volumes of 3-methylpyridine solutions

摘要

Densities of 3-methylpyridine (3-MP) + water and 3-methylpyridine + heavy water were measured in the 3-MP mole fraction range 0.002-0.04 from 298 to 318 K. The excess molar volumes of 3-MP + D2O mixtures were found to be more negative than those of 3-MP + H2O mixtures. The partial molar volume of 3-MP at infinite dilution is smaller in D2O than in H2O which suggests that 3-MP causes a structure-breaking effect in water which is more pronounced in D2O. It was found that the volume change with concentration in dilute solutions of 3-MP in water and heavy water can be adequately described by the pair-wise interaction of the solute molecules. The molal volume second-virial coefficient, V-xx, is positive indicating that the water molecules are less structured in the cospheres of the solute pairs than in the bulk solvent. The temperature dependence of V-xx displays a maximum at around 308 K in the case of D2O solutions, whereas V-xx increases almost linearly with temperature in H2O solutions.