Dissolution behaviour and thermodynamic properties of rubidate in (methanol + water) and (ethanol + water) mixtures from T = (278.15 to 318.15) K

Abstract Due to the poor water solubility of rubidate, it is difficult to prepare and apply. In this work, the objective is to study the dissolution behaviour of rubidate in (methanol + water) and (ethanol + water) mixtures and calculate apparent thermodynamic properties. In selected two mixtures, it increased monotonically with the increasing mass fraction of alcohols at all researched temperatures. When the mass fraction of alcohol is more than w=0.5, the solubility increases sharply, and the largest mole solubility data was found in pure alcohols (3.344×10-2 in methanol at 318.15K, and 5.506×10-2 in ethanol), the minimum data was in pure water (0.581×10-6 at 318.15K), an increase of 5.76×104 folds in methanol aqueous, and 9.48×104 folds in ethanol aqueous. The commonly used thermodynamic models (Jouyban-Acree model and CNIBS/R-K model) were used to correlate the experimental results. Because the relative average deviation (RAD) of two models was more than 5%, the calculated value by two models was further evaluated with residual value analysis. In the following, the analysis of apparent thermodynamic properties indicated that the dissolution process is apparently not only endothermic but also entropy-driving. The study on the dissolution behaviour of rubidate in alcohol aqueous is helpful to optimize the preparation and purification process.