# Distribution constant

﻿
Distribution constant

The distribution constant (or partition ratio), is the equilibrium constant for the distribution of an analyte in two immiscible solvents.[1] For a particular solvent, it is equal to the ratio of its molar concentration in the stationary phase to its molar concentration in the mobile phase, also approximating the ratio of the solubility of the solvent in each phase. The term is often confused with partition coefficient or distribution coefficient, and is often represented by KD.

## Expression

The ratio of activities of a solute, A in an aqueous/organic system will remain constant and independent of the total quantity of A (hence $[A]_{org} \propto [A]_{aq}$), so at any given temperature:

$(K_D)_A = {(a_A)_{org} \over(a_A)_{aq}} \approx {[A]_{org} \over[A]_{aq}}$

Distribution constants are useful as they allow the calculation of the concentration of remaining analyte in the solution, even after a number of solvent extractions have occurred. They also provide guidance in choosing the most efficient way to conduct an extractive separation.

Thus, the concentration of A remaining in an aqueous solution after i extractions with an organic solvent can be found using:

$[A]_i = ({V_{aq} \over V_{org} K_D + V_{aq}})^i [A]_0$

(where [A]i is the concentration of A remaining after extracting Vaq millilitres of solution with the original concentration of [A]0 with i portions of the organic solvent, each with a volume of Vorg).

## References

1. ^ Rice, N. M.; Irving, H. M. N. H.; Leonard, M. A. (1993), "Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)", Pure and Applied Chemistry 65 (11): 2373, doi:10.1351/pac199365112373

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• distribution constant — Смотри константа распределения …   Энциклопедический словарь по металлургии

• distribution — See asymmetic power distribution asymmetrical power distribution constant power distribution equal power distribution load controlled power distribution load distribution calculation load distribution power distribution static high voltage… …   Dictionary of automotive terms

• Constant false alarm rate — (CFAR) detection refers to a common form of adaptive algorithm used in radar systems to detect target returns against a background of noise, clutter and interference. Other detection algorithms are not adaptive. Non adaptive detectors are… …   Wikipedia

• Distribution De Weibull — Weibull Densité de probabilité / Fonction de masse Fonction de répartition …   Wikipédia en Français

• Distribution de weibull — Weibull Densité de probabilité / Fonction de masse Fonction de répartition …   Wikipédia en Français

• Constant voltage speaker system — Constant voltage speaker systems refer to networks of loudspeakers which are connected to an audio amplifier using step up and step down transformers to simplify impedance calculations and to minimize power loss over the speaker cables. They are… …   Wikipedia

• DISTRIBUTION (économie) — Pour la Chambre de commerce internationale, la distribution est «le stade qui suit celui de la production des biens à partir du moment où ils sont commercialisés jusqu’à leur prise en possession par le consommateur ou l’utilisateur final. Elle… …   Encyclopédie Universelle

• Distribution law — [1] or the Nerst s distribution law gives a generalisation which governs the distribution of a solute between two non miscible solvents.This law was first given by Nerst who studied the distribution of several solutes between different… …   Wikipedia

• distribution theory — ▪ economics Introduction       in economics, the systematic attempt to account for the sharing of the national income among the owners of the factors of production land, labour, and capital. Traditionally, economists have studied how the costs of …   Universalium

• Distribution de Weibull — Weibull Densité de probabilité / Fonction de masse Fonction de répartition …   Wikipédia en Français