Solvent activity in (Ag, Tl)NO3–dimethyl sulfoxide liquid mixtures from vapour-pressure measurements

Abstract

An investigation of the liquid (Ag_0.5Tl_0.5)NO₃–dimethyl sulfoxide system has been performed over a wide composition range 0.05 < x < 0.80, where x is the mole fraction of salt in the mixture, at temperatures in the interval 360 < T/K < 390, by means of vapour-pressure measurements on a dew-point apparatus. The thermodynamic activity of the solvent is found to exhibit a markedly negative deviation from Raoult's ideal behaviour in contrast to the positive deviation previously found for the (Ag_0.5Tl_0.5)NO₃–water system. The extended composition range investigated allows a comparison to be made between different wide-range solution models, such as those of Stokes and Robinson, Pitzer and Simonson and Horsák and Sláma, based on different fundamental assumptions. A substantial agreement is found in their ability to fit data in the high salt concentration range, so that all three models can be used to calculate thermodynamic properties by extrapolation to infinite dilution of the ‘solvent’ in the liquid salt.