Some properties of binary aqueous liquid mixtures. Apparent molar volumes and heat capacities at 298.15 K over the whole mole fraction range

Abstract

Densities and molar heat capacities have been measured for the following binary systems at 298.15 K: water + formamide, water +N,N-dimethylacetamide, water + dimethylsulphoxide and water + acetonitrile over the whole mole fraction range. From these data apparent molar volumes and heat capacities have been calculated for both water and the organic components. The volumes have been discussed in terms of enhanced water–water interactions and as being the result of inter-component interaction. The volume of water infinitely diluted in the various solvents might be well understood from the packing of hard sphere molecules. Similar reasoning cannot be applied to the heat capacities. Most of the curves are typical for weakly hydrophobic solutes, while the apparent molar heat capacity curve of formamide in water + formamide resembles that of hydrophilic solutes. Finally, the apparent molar heat capacities of water at infinite dilution in the various solvents are unexpectedly high.