Isopiestic Method for Solution Model Verifications and Binodal Determinations

Testing a theoretical model by using precise experiments is one of the important subjects in natural sciences. The isopiestic method at constant temperature is one of the most important and widely used experimental methods for determining thermodynamic properties of aqueous solutions. It has been used for the precise measurements of solvent activities and solute molalities for hundreds of binary and higher-order aqueous solutions. It has also been applied to a few binary nonaqueous solutions. On the other hand, the Zdanovskii–Stokes–Robinson (ZSR) rule is the simplest isopiestic molality relation for mixed electrolyte and nonelectrolyte aqueous solutions related to the corresponding single aqueous solutions and thus the isopiestic method has been used as the perfect experimental method for its direct and precise verifications. Here, we review our isopiestic measurements used for solution model verifications. The experimental systems include unsaturated and saturated aqueous solutions, unsaturated methanol solutions, unsaturated mixed solvent systems, unsaturated liquid alloys, unsaturated molten salt mixtures, and unsaturated molten oxide mixtures. Additionally, the isopiestic principle and preliminary experiments are also described for the binodal determination of liquid–liquid bi-phasic solutions, taking binary liquid alloys as examples.