Chemical Equilibrium and Critical Phenomena: Solubility of Indium Oxide in Isobutyric Acid + Water Near the Consolute Point

• Published in: Journal of chemical and engineering data 2009-05, Vol.54 (5), p.1537-1540
• Main Authors: Hu, Baichuan, Richey, Randi D, Baird, James K
• Format: Article
• Language: English
• Subjects: Chemical thermodynamics; Chemistry; Exact sciences and technology; General and physical chemistry; Mixtures; Solubility; Solutions; Thermodynamic properties
• ISSN: 0021-9568; 1520-5134
• DOI: 10.1021/je8008599

We have determined the solubility, s, of indium oxide in the liquid mixture isobutyric acid + water along the critical isopleth at temperatures above the upper critical solution temperature near 299 K. When plotted in van’t Hoff form with ln s vs 1/T, the measurements of solubility lie on a straight line for values of the absolute temperature, T, which are sufficiently in excess of the critical solution temperature, T c. The sign of the slope, (∂ ln s/∂(1/T)), indicates that the enthalpy of dissolution is endothermic. When the temperature is within 1 K of T c, however, the slope departs from its constant value and appears to diverge toward negative infinity. The principle of critical point universality predicts that a divergence in (∂ ln s/∂(1/T)) is to be expected for T near T c in those cases where the stoichiometry of the dissolution reaction involves both components of the solvent; moreover, the Gibbs−Helmholtz equation predicts that if the enthalpy of solution is endothermic, the sign of the divergence should be negative. Both of these predictions are confirmed by the experimental data.