DISTRIBUTIONS LAW

From Big Medical Encyclopedia

DISTRIBUTIONS LAW — the law, according to Krom the substance capable to be dissolved in two immiscible liquids which are in contact and in balance with each other is distributed between these liquids so that the size of the relation of its concentration (distribution coefficient) at an invariable temperature remains to a constant irrespective of total quantity of solute. River z. is the cornerstone of the theory and practice of extraction from solutions of various substances, including and biologically active, methods of extraction (see) and a partition chromatography (see); it is established also that the distribution coefficient of substance between oil and water phases is higher, the better this substance gets through biol, membranes. River z. finds broad application in pharmacology, medicobiological, biochemical and other researches.

River z. it is open Twirled (M. R. by E. Berthelot) and E. C. Jungfleisch in 1872 and W. H. Nernst in 1890 is confirmed experimentally and theoretically.

Mathematically R. z. it is expressed by the following equation:

(C1/C2) = K,

where C1 and C2 — concentration of substance in the first and second liquids, mol/l; To — the constant called by a distribution coefficient or a constant of distribution. It is possible to give a case of dissolution of iodine in water and chloroform as an example. The distribution coefficient of iodine between these solvents is equal to 130. It means that if to water, in a cut iodine is dissolved to add the chloroform which is not mixing up with it and to shake up, and then to allow to be defended, then after establishment of balance between phases concentration of iodine in chloroform will be 130 times higher, than in water, irrespective of total quantity of iodine.

The equation (C1/C2) = is carried out by K under a condition if a pier. the weight (weight) of solute in two liquids is identical. The distribution coefficient depends by nature immiscible liquids, the nature of the substance dissolved in them, a so-called third component, and on temperature.

Since solubility of substance in liquid is measured by concentration of its saturated solution in this liquid at this temperature, the equation can be replaced with the relation of S1/S2 = K where S1 and S2 — solubility of substance in two immiscible liquids.

If in one of immiscible liquids of a molecule of solute are exposed to dissociation or association, then the equation (C1/C2) = K, can look as follows: (C1n/C2) = K, where n — the size of the relation of averages a pier. scales of solute in the second and first liquids.


Bibliography: Kireev V. A. Short course of physical chemistry, page 327, etc., M., 1978; To about t y to And. and I am a N and h e to To. Membrane transport, the lane with English, page 189, etc., M., 1980.

V. P. Mishin.

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