Solubilities, Fugacities and All That in Solution Chemistry

Solution chemistry is at the heart of many research areas in the pure and applied sciences. In fact, for more than a century, experimental as well as theoretical work on solution properties and phase equilibria involving liquid/fluid solutions in general, and aqueous liquid/fluid solutions in particular, have held prominent positions in (bio-)physical chemistry. The scientific insights gained thereby are invaluable and have not only contributed decisively to the creation of the formal structure of chemical thermodynamics but have also paved the way for the development of practically useful molecular-based models describing real solution behavior. In the first part of this review, I shall present a concise overview of the thermodynamic formalism relevant in solubility studies on liquid/fluid nonelectrolyte systems. In the second part, selected aspects of solubility data reduction and data correlation will be touched upon, including a critical evaluation of some popular approximations and a survey of current estimation technique for indispensable auxiliary quantities, such as virial coefficients and partial molar volumes at infinite dilution. One of the goals will be to clarify issues frequently overlooked and to dispel misconceptions encountered in the literature. Pride of place will be given to the Henry fugacity (also known as Henry's law constant), which is one of the most misunderstood thermodynamic quantities, and to various caloric quantities derived via van't Hoff analysis of high-precision solubility data.