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Three Component Phase Diagram of the Water-Heptane-Propanol System. Illustrate your essay with specific examples.

A convenient way of illustrating the principles governing phase changes within three component systems is to use a partially miscible liquid system. In the past, the acid-chloroform-water system has been employed as a practical example to investigate ternary systems and the miscibility gap (Wright et al., 1891; Brancker et al., 1940). However, since the status of chloroform has been changed to a suspected carcinogen, these experiments have been rendered unsuitable for teaching laboratories. A fitting alternative is offered in the form of an alcohol-water-hydrocarbon system (Washburn et al., 1931). Two undergraduate laboratory experiments have been proposed in the past, based on the water-n-heptane-n-propanol system and are similar to the previously popular acid-chloroform-water experiments. However, whereas the acid-chloroform-water experiments solely involve titration, these experiments utilise other techniques. Udale and Wells (1995) outline a method whereby a phase diagram can be constructed based upon titration results but also describe how pairs of phases in equilibrium can be quantified chromatographically. Karukstis et al. (2000) describe a novel method whereby the phase diagram is determined spectroscopically. The following suggested experimental procedure describes both methods, aimed at teaching students the principles of i) Gibbs phase law ii) phase diagrams iii) the three component system and iv) the miscibility gap.

Gibbs phase law

The number of degrees of freedom, F, within a system is given by:

Thin layer Chromatography (Tlc) stage 2

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