Nernst's distribution law

What is the Nernst's distribution law?

The Nernst's distribution law (or Nernst's partitioning law) was enunciated by Nernst and explains how a solute will be distributed between two immiscible solvents. It is a concept widely used in solutions of immiscible liquids.

If we have two non-miscible solvents and we add a solute to them, this will be distributed between them in such a way that it is fulfilled that:

"the ratio between solute concentrations (C) in the two non-miscible liquids is going to be a constant, independent of the amount of solute added, and equal to the ratio between their respective solubilities (S)."

ley de distribución de Nernst de reparto concentracion solubilidad temperatura constante

where Kd is the distribution constant.

Examples

Iodine is approximately 85 times more soluble in CCl4 than in water, or in other words, we can have the same amount of iodine in water as in 85 times less CCl4.

This property allows us to extract all the iodine from water using CCl4. This process is called extraction.

How is greater efficiency achieved in an extraction process?

  • Increasing the number of extractions.
  • Making the volumes used of the extracting solvent (CCl4) as small as possible.