Distribution law or the Nernst's distribution law
gives a generalisation which governs the distribution of a solute between two immiscible solvents. This law was first given by
Nernst who studied the distribution of several solutes between different appropriate pairs of solvents.
C
1/C
2 = K
d
Where K
d is called the
distribution coefficient
In the physical sciences, a partition coefficient (''P'') or distribution coefficient (''D'') is the ratio of concentrations of a compound in a mixture of two immiscible solvents at equilibrium. This ratio is therefore a comparison of the solub ...
or the partition coefficient.
Concentration of X in solvent A/concentration of X in solvent B=Kď
If C
1 denotes the
concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number concentration'', ...
of
solute
In chemistry, a solution is defined by IUPAC as "A liquid or solid phase containing more than one substance, when for convenience one (or more) substance, which is called the solvent, is treated differently from the other substances, which are ...
X in
solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
A & C
2 denotes the
concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number concentration'', ...
of solute X in solvent B; Nernst's distribution law can be expressed as C
1/C
2 = K
d. This law is only valid if the solute is in the same molecular form in both the solvents. Sometimes the solute dissociates or associates in the solvent.
In such cases the law is modified as,
D(Distribution factor)=concentration of solute in all forms in solvent 1/concentration of solute in all forms in solvent 2.
Further reading
* Martin's Physical Pharmacy & pharmaceutical sciences; fifth edition, Patrick.J.Sinko , Lippincott Williams & Wilkins. Note, this source does not describe Nernst in the manner the text presents, nor is it evident that it is the source of the quotation (as much as one can surmise through search). Lacking full information (i.e., page number), the source is moved to Further reading.
References
{{DEFAULTSORT:Distribution Law
Equilibrium chemistry
Walther Nernst