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, Tc. 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 Tc, 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 Tc 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.
Compounds
#
Formula
Name
1
In2O3
diindium trioxide
2
C4H8O2
2-methylpropanoic acid
3
H2O
water
Datasets
The table above is generated from the ThermoML associated json file (link above).
POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied;
the numbers refer to the table of compounds on the left.