Physical–Chemical Properties of Ionic Liquid-Containing Mixtures

To know the properties of a system means to know the state of such system. Intensive molar quantities are used to characterize matter and to compare characteristics of different substances. The differences in the behaviour of different substances are attributable to their physical–chemical properties. In the systematic study of the properties of a class of compounds it is helpful to recognize that within homologous series, properties usually vary in a regular way, eventually with a few exceptions. The systematic study of physical–chemical properties of ionic liquids, ILs, is a very hard task as the term IL indicates many different classes having properties values that vary in a very wide range. Measurements carried out on ILs having very often an high viscosity, are particularly delicate and discrepancies in the results may be ascribed, at least partially, to problems of reproducibility of the thermodynamic states. In this chapter we will consider fundamental and derived volumetric and calorimetric properties of pure ionic liquids and their mixtures with a molecular solvent of known qualitative and quantitative composition. Some results, taken from the literature are here reported but an exhaustive survey of the current knowledge in the field of ILs’ characterization has not be reached.