Thermodynamic and¹⁹F NMR studies of antimony trifluoride in water

Abstract

Densities, specific heat capacities per unit volume and enthalpies of dilution at 25°C and osmotic coefficients at 37°C were measured for antimony trifluoride in water as functions of concentration. From the first three properties the apparent and partial molar volumes, heat capacities and relative enthalpies were derived. As well, pH measurements in water at 25°C and¹⁹F NMR spectra in water and methanol at 33°C were also carried out. All the thermodynamic properties together with the chemical shifts abruptly change in the very dilute concentration region (<0.1m) and, then, tend to a constant value. These trends have been rationalized through a simple model based on an equilibrium of dissociation of SbF₃ into two ionic species. From the simulation of all the data it is derived that two concomitant equilibria are present in solution: the hydrolysis process of SbF₃ which explains the pH values and the ionic dissociation of SbF₃ which accounts for the¹⁹F NMR data.