Distribution Law - Definition, Assumptions & Limitations

The distribution law, also known as Nernst’s distribution law, states that when a solute is distributed between two immiscible solvents at a constant temperature, the ratio of its concentrations in the two solvents is constant.
- - - - $\frac{[\text{Solute}]_A}{[\text{Solute}]_B} = K_d$
$[\text {Solute}] _A \quad \text{and} \quad [\text {Solute}] _B$
are the concentrations of the solute in solvents A and B, respectively.
K_d is the distribution coefficient or partition coefficient

Chemical Changes: If the solute reacts chemically or changes state in one of the solvents, the law doesn’t apply.
Solvent-Solvent Interaction: Even slight miscibility between solvents can affect the partition coefficient.
Temperature Variations: Changes in temperature can alter the partition coefficient, affecting distribution.
Concentration Dependence: High concentrations can lead to solute saturation or self-interaction, deviating from expected behaviors.
Physical Form Variations: Differences in solute ionization or physical state between solvents can impact distribution.

Drug Design and Pharmacokinetics: Essential for understanding drug distribution across body compartments, impacting dosing and delivery.
Environmental Science: Helps predict the movement of pollutants between phases like water and oil.
Extraction Processes: Guides the selection of solvents for efficient compound extraction in chemical and pharmaceutical industries.
Analytical Chemistry: Basis for solvent choice in liquid-liquid extraction, optimizing separation of analytes.
Food Industry: Influences the formulation by predicting how additives distribute between different phases.