Graphical representation of solid-solute phase equilibria in aqueous solution

Solid-solute phase diagrams are useful tools for the depiction of stable and metastable equilibria between binary mixed crystals with common ions and aqueous solutions. Generalized Gibbs-Duhem equations provide the common basis and suggest natural co-ordinates for the graphical representation of thermodynamic variables. Diagrams applicable even to highly soluble electrolytes can be constructed by plotting the osmotic coefficient of the solvent times the total molality πΣm vs. the mole fractions x of the dissolved and solid components, respectively. According to Schmalzried and Pelton's topological classification the resulting phase diagrams are of Type II. They can be used for practical purposes, e.g., to predict the separability of the components by fractional crystallization