Additional Methods Liquids and Solutions

Pure liquids and solutions have probably received a major portion of the experimental effort devoted to the nonspectroscopic methods of detection. The liquid phase is susceptible to simple techniques and is the naturally occurring state for many substances. The principal methods of study are vapor pressure measurements, cryoscopy, solubility, and partition studies. To a lesser degree parachor, refractive index, thermal and acoustic conductivity, osmotic pressure, and magnetic susceptibility measurements have been applied to H bonded materials. Unfortunately, the difficulty of giving an adequate description of the liquid state sometimes produces problems of interpretation. 

1 Vapor Pressure, Boiling Points, and Azeotropes. Turning to solutions, the interaction or interference between molecules is revealed in plots of composition vs, vapor pressure or boiling point. Deviation from ideal behavior produces curves with maxima or 

Harrison, and Berg (627) devised a compact classification based on the H bonding ability of generic classes of organic compounds. It allows qualitative prediction of the formation (or absence) of azeotropes and their types and, as our later sections and chapters show, it is useful for correlating other properties. Table 2-IX defines a classification scheme based heavily on their idea. This classification will be used throughout this book. 

Agreement with Raoult s Law is not a sufficient condition for ideality —though it is a necessary one (627). Occasionally a mixture capable of H bonding will form a pseudo-ideal system which obeys the equation. Pyridine-ethanol is an example (227) which must include H bonding, both in association of the alcohol and between the two components. The observed ideal behavior surely results from a fortuitous cancellation of effects. 

Mainly halogenated compounds with enough halogens to activate the hydrogens CHCU, G2HGlj, etc. and possibly G2H2 protons 

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