Representation of Volumetric and Compressibility Properties in Binary and Ternary Systems

Thermodynamic properties of solutions in binary and ternary aqueous systems which are derived from very accurate measurements of density and its changes with concentration, temperature and pressure, are examined in a detail. Precise definitions of the apparent molar volumes, the apparent molar expansibilities and the apparent molar compressibilities of components in ternary solutions are discussed. The significance of errors caused when inexact formulas are used is illustrated. It is demonstrated that in ternary solutions, an experimental procedure leading to determination of the mean apparent molar volume is superior than that based on the reduction to pseudo-binary systems. The present author proposed a new two-parameter empirical equation which correlate and predict densities in binary aqueous solutions. This equation includes densities of pure water at temperature T and two adjustable parameters which are practically independent of temperature. The expected accuracy of predicted in aqueous solutions densities makes this equation most suitable for engineering calculations.