Distribution Law

It is observed that when a solid or a liquid is added to a mixture of two immiscible liquids, in both of which it is soluble (e.ge., iodine to a mixture of carbon disulphide and water or succinct acid t a mixture of ether and water), it distributes itself between the two liquids in such a manner that eh ratio of concentrations of the substance in the two liquids is always contestant at content temperature. These observations were made by Berthelot and Jungfleisch in 1872. However, it was pointed out by Nernst in 1891 that he ratio of the concentrations I content only when the solute has the same molecular weight (i.e., the molecular state) in both solvents. Hence the generalization was put I a proper form by Nernst and is called Nernst Distribution Law. It states as follows:

‘A solute (solid or liquid) distributes itself between the two immiscible solvents in such a way that the ratio of the concentrations* of the solute in the two solvents is constant at constant other molecular species presents, provided that he solute has the same molecular state in both the solvents.’

           Distribution of solute X
           between immiscible solvents
           A and B

Thus if a solute X distributes itself between the two immiscible solvents A and B, then if X remains in the same molecular state in both the solvents, we will have

The constant K is called Distribution coefficient or Partition coefficient.

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