Volumetric and optical study of molecular association in binary mixtures of dimethyl sulphoxide with carboxylic acid

Abstract

Density and refractive index have been measured for the binary mixture of dimethyl sulphoxide (DMSO) with propanoic acid and n-butyric acid at three temperatures, 293, 303 and 313 K, over the entire composition range. Excess parameters such as excess molar volume (V E) and molar refraction deviation (ΔR m) have been calculated from the measured density and refractive index to study the molecular association between the component molecules. The V E and ΔR m values of these mixtures were fitted to the Redlich–Kister polynomial equation. Both excess parameters were plotted against the mole fraction of DMSO over the whole composition range. The values of V E and ΔR m have been found to be negative for both mixtures over the entire composition range, which suggests the presence of strong intermolecular interaction. The experimental refractive data of these mixtures were also used to test the validity of the empirical relations for the refractive index.