Nernst Distribution Law

Introduction

This law was given by Nernst in the year 1891. As the name suggests, it is related to the distribution of a solute(solid or liquid) in two non-miscible solvents. However, it dissolves in both of them.

Nernst Distribution Law

According to the law,

” if a solute “X” distributes between two non-miscible solvents ‘a’ and ‘b’ at a constant temperature and “X” is in the same molecular for in both of them, then the ratio of the concentrations of “X” in he two solvents is a constant quantity ”

i.e.                       Concentration of “X” in solvent ‘a‘ =  C1 =  K (constant)                             Concentration of “X” in solvent ‘b’ = C2

The constant K is called the partition coefficient and is also denoted by Kd ( distribution constant)

For example, Iodine a violet cyrstalline solid when added to a mixture of two immiscible liquids water and carbon tetrachloride, distributes in both of them. The value of K in this case is 85 at room temperature i.e. 298 K.

Applications

The priniciple of distribution law is quite helpful in metallurgical operations. A popular example is Desilverisation of Lead(Parke’s process). But more about that will be taken up in the later posts of this blog.

Limitations

There are basically two limitations. They are – :

1. The solute which is to be distributed should not react with any of the solvents.

2. The solute should not undergo any change in its molecular state in the solvents i.e. it should neither dissociate nor associate.