Nernst distribution law: its derivation and applications.
Answers
Answer:
“When a solute is taken up with two immiscible liquids, in both of which the solute is soluble, the solute distributes itself between the two liquids in such a way that the ratio of its concentration in the two liquid phases is constant at a given temperature provided the molecular state of the distributed solute is same in both the phases”.
I.e.
\dfrac{C_1}{C_2} = K_D
Where C_1 \text{and} C_2 are the concentrations of the solute in two phases. K_D is called distribution coefficient or partition coefficient.
(A) When solute undergoes association in one of the solvents, we have
K_D = \dfrac{C_1}{n \sqrt{C_2}} or K_D = \dfrac{n \sqrt{C_1}}{C_2}
Where ‘n’ =order of association.
(B) When solute undergoes dissociation, we have
K_D = \dfrac{C_1}{C_2 (1- \alpha)} \text{or} K_D = \dfrac{C_1 (1- \alpha)}{C_2}
Where \alpha= on degree of dissociation.
(C) When solute is to be extracted from solution by another suitable solvent, we have.
Amount left unextracted = W[ \dfrac{K_DV}{K_DV + v_1}]^n
Where ‘W’ =Initial amount present in solution, ‘V’ =volume of solution, v_1 volume of extracting solvent, K_D = Distribution coefficient, ‘n’ = Number of extraction operations.
Application:
The applications of Nernst Distribution Law-
1)Solvent extraction.
2)patrtion chromatography.
3)release of drug from dosage forms.
4)passase of drug through membranes.
5)preservstion of emulsions and creams.
6)formation of solubilized system.