Question

State Distribution Law and give its three

applications.

Answer 1

Distribution law or the Nernst’s distribution law gives a generalization which governs the distribution of a solute between two non miscible solvents. This law was first given by Nernst who studied the distribution of several solutes between different appropriate pairs of solvents. The statement of the law is:
"If a solute X distributes itself between two non miscible solvents A & B at constant temperature & X is in the same molecular condition in both the solvents, then: concentration of X in A / Concentration of X in B = Kd".
Where Kd is called the distribution coefficient or the partition coefficient. If C1 denotes the concentration of solute in solvent A & C2, the concentration of X in B; Nernst’s distribution law can be expressed as C1/C2 = Kd.
Applications of Nernst’s Distribution law:
1) solvent extraction;
2) partition chromatography; 
3) release of drug from dosage forms;
4) passage of drug through membranes; 
5) preservation of emulsions and creams; 
6) formation of solubilized system.

Answer 2

Explanation:

The distribution law states that a solute gets distributed between the two layers of immiscible solvents in such a way that the ratio of its concentration in each solvent becomes equal to the ratio of its solubility.

The formula for distribution law is as follows.

                    $K_{d}$ = $\frac{C_{0}}{C_{w}}$

where,  

                    $C_{0}$ = molar concentration in organic layer

                    $C_{0}$ = molar concentration in aqueous layer

                    $K_{d}$ = distribution coefficient or constant

Applications of distribution law states are as follows.

• Solubility of a solute can be measured.
• One substance can be extracted from the solution containing various substances.
• Used in high performance liquid chromatography.