Measurement and modelling of liquid density (298.15 and 313.15 K) and vapour pressure osmometry (313.15 K) for binary aqueous solutions of organic salts

Abstract

Due to the eco-friendliness of organic salts, they have been gradually replacing other electrolytes in different fields of chemistry. For example, they provide biocompatible salting -out agents for liquid-liquid extractions and earth -abundant materials for flow batteries. Nevertheless, reliable liquid density and vapour pressure data, which are paramount for a proper parameterisation of thermodynamic models, are often hard to find for aqueous solutions of organic salts, delaying the development of these technologies. In this work, the liquid density (p ) of five binary aqueous solutions of organic salts (disodium tartrate, sodium potassium tartrate, dipotassium tartrate, trisodium citrate and tripotassium citrate) were measured and correlated at 298.15 and 313.15 K and 0.1 MPa. In these assays, second-degree polynomials provided determination coefficients ( R 2 ) larger than 0.9982 in the correlation of liquid density with salt molality, for which a very accurate description of this property was accomplished. Moreover, vapour pressure osmometry (VPO) studies were carried out for these solutions at 313.15 K and 0.1 MPa. Then, the obtained osmotic coefficients ( o ) were successfully modelled using the Extended Pitzer Model of Archer, yielding standard deviations (c o ) lower than 8.61 & sdot; 10 -3 . Finally, the mean molal activity coefficients ( y +/- ) and excess Gibbs free energies ( G E /RT ) of the binary aqueous solutions of organic salts were effectively calculated, with potassium- and tartrate -based salts attaining significantly higher values than the ones composed of sodium and citrate, hinting at a more ideal solution behaviour of the former.