Aqueous solutions of nonelectrolytes

The liquid state is one of the three principal states of matter and arguably the most important one, the main reasons being the following: (I) the majority of chemical synthesis reactions are liquid-state reactions; (II) separation processes, such as distillation, extraction, and fractional crystallization, are based on vapor–liquid equilibria, liquid–liquid equilibria, and solid–liquid equilibria, respectively, all involving multicomponent mixtures/solutions; (III) when focusing on water as solvent, we note that it is the most abundant substance on the surface of the earth, and being the principal constituent (about 70% by weight) of all living organisms, it is essential for life as we know it. Thus, it is not surprising at all that experimental as well as theoretical work on nonelectrolyte solutions in general, and on aqueous solutions of nonelectrolytes in particular, have held prominent positions in (bio-)physical chemistry for more than a century. The insights thereby gained have contributed decisively to build the formal structure of chemical thermodynamics and have paved the way for the development of practically useful real-solution models needed in chemical engineering. In this review, first the thermodynamic formalism relevant for solubility studies as well as a critical discussion of some popular approximations will be presented concisely. Estimation methods for auxiliary quantities, such as virial coefficients and partial molar volumes at infinite dilution, will be briefly indicated, followed by a summary of rational strategies for data reduction and data correlation. Finally, a few eclectically chosen results obtained for dilute aqueous solutions of nonelectrolytes will be linked to hydrophobic effects, which are generally accepted to play an important role in a wide variety of biological processes.