Sound velocity measurements in the water + acetonitrile system at temperatures from 293.15 to 323.15 K and its implications on thermodynamic data processing

Abstract

It has been claimed that partial molar volumes of water + acetonitrile (AN) mixtures show extremes at AN-rich mixtures. Since partial molar volumes are obtained by differentiation of curves fitting experimental data, it was deemed reasonable to check if such a discontinuity exists. With this goal, density and sound velocity have been measured over the whole composition range at 293.15, 298.15, 303.15, 308.15, 313.15, 318.15 and 323.15 K. From these values, isentropic compressibility and intermolecular free lengths, as well as excess quantities for sound velocity, isentropic compressibility and intermolecular free length have been calculated. Density values are in good agreement with previous published values and a minimum in isentropic compressibility appears at around 0.04 mole fraction of AN. This behaviour is not consistent with the claim that inflection points occur in the density curve at high AN content.

Keywords:

• sound velocity
• density
• water–acetonitrile
• isentropic compressibility
• intermolecular interaction
• excess properties

Acknowledgements

The authors thank the Fondo para la Investigación Científica y Tecnológica for financial support to this project through PICT 38 467 and the Universidad de Buenos Aires through UBACYT 90 100 270.