When a solute distributes itself between two immiscible solvents in equilibrium, then the ratio of its concentration in the two solvents remains constant. This is known as the Distribution Law.
Example: The solute iodine distributes itself in CCl4 and water solvents. Let C1 and C2 be the concentration of I2 in CCl4 and water respectively. Then from the Distribution Law:
C1 / C2 = KD
Where KD is the partition coefficient. The value of KD depends upon the temperature, nature of the solute, nature of the two solvents, and the manner in which the constant is expressed (i.e., C1/C2 or C2/C1).
Essential Conditions for the Distribution Law
- Temperature must be constant throughout the experiment.
- The solutions must be dilute.
- The two solvents should be completely insoluble or very sparingly soluble, and their mutual solubility should not be affected by the presence of the solute.
- The solute must not undergo dissociation, association, or chemical interaction with any of the solvents.