Solubility of Partially Miscible Liquids

Conjugate solutions:  Many liquids are partially miscible and form two liquid layers at a particular temperature. Such liquid solutions in which different compositions of components coexist are called conjugate solutions, for example, phenol and water.

Critical temperature: The miscibility of liquids varies with temperature. At a certain temperature the two layers become completely miscible. This temperature is called critical temperature or consolute temperature

Azeotropic Mixture

An azeotropic mixture is a mixture of two liquids having the same boiling point. These two liquids cannot be separated by simple distillation because of similar boiling point of the liquids. These mixtures are thus called constant boiling mixtures. These are formed by non-ideal solutions.

Azeotropic mixture and composition curves:

  • These are the mixture of two liquids which boils at one particular temperature like a pure liquid and distils over in the same composition i.e., these are constant boiling mixtures. These are formed by non­ideal solutions.
  • The study of the vapour pressure curves of such miscible liquids is of great help in separating the constituents of the liquid mixtures by distillation.
  • The separation by fractional distillation is possible only when the vapour phase has a composition different from that of the boiling liquid mixture.
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