Correlation of the solvation properties of water and dimethyl sulphoxide in metal nitrate–water and metal nitrate–dimethyl sulphoxide melts with the molecular properties of the constituents of the melts

Abstract

The currently available thermodynamic data obtained by vapour pressure measurements on highly concentrated solutions of single-metal nitrates in water and in dimethyl sulphoxide are numerous and reliable enough to allow us to establish a correlation between the standard solvation free energy, ΔG^°_sv, of water and dimethyl sulphoxide in (undercooled) liquid nitrates and some of the molecular and ionic parameters which characterize the two molecules and the ionic constituents of the salts. To supplement the previously investigated systems, the system AgNO₃–DMSO has been studied by vapour pressure measurements on a dew-point apparatus over the temperature range 330 < T/K < 375 with the salt mole fraction, x, ranging between 0.15 and 0.40. The widely used Stokes–Robinson adsorption–hydration theory has been employed to treat the experimental results and to calculate the values of ΔG^°_sv. Reasonable linear correlations have been found between ΔG^°_sv and a function relating the electrostatic cation–dipole interaction energy with physical parameters (charge numbers, ion–dipole distances), suggesting that solvation of both water and dimethyl sulphoxide in liquid nitrates is governed mainly by the cation–dipole electrostatic interaction energy. The roles of the dipole moments and of the donating abilities of the two molecules are pointed out and some suggestions are made concerning the contribution of other energetic and entropic factors to the solvation processes.