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Sorption refers to the action of both absorption and adsorption taking place simultaneously. As such it is the effect of gases or liquids being incorporated into a material of a different state and adhering to the surface of another molecule. Absorption is the incorporation of a substance in one state into another of a different state (e.g., liquids being absorbed by a solid or gases being absorbed by a liquid). Adsorption is the physical adherence or bonding of ions and molecules onto the surface of another molecule.


Laboratory absorber. 1a): CO2 inlet; 1b): H2O inlet; 2): outlet; 3): absorption column; 4): packing.

Absorption, in chemistry, is a physical or chemical phenomenon or a process in which atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. This is a different process from adsorption, since molecules undergoing absorption are taken up by the volume, not by the surface (as in the case for adsorption). A more general term is sorption which covers adsorption, and ion exchange. Absorption is basically where something takes in another substance.[1]

If absorption is a physical process not accompanied by any other physical or chemical process, it usually follows the Nernst partition law:

"the ratio of concentrations of some solute species in two bulk phases in contact is constant for a given solute and bulk phases"[citation needed];
\frac{[x]_{1}}{[x]_{2}} = constant = K_{N(x,12)}

The value of constant KN depends on temperature and is called partition coefficient. This equation is valid if concentrations are not too large and if the species "x" does not change its form in any of the two phases "1" or "2". If such molecule undergoes association or dissociation then this equation still describes the equilibrium between "x" in both phases, but only for the same form - concentrations of all remaining forms must be calculated by taking into account all the other equilibria.[1]

In the case of gas absorption, one may calculate its concentration by using e.g. the Ideal gas law, c = p/RT. Alternatively, one may use partial pressures instead of concentrations.

In many technologically important processes, the chemical absorption is used in place of the physical process, e.g. absorption of carbon dioxide by sodium hydroxide - such processes do not follow the Nernst partition law.

For some examples of this effect see liquid-liquid extraction, it is possible to extract from one liquid phase to another a solute without a chemical reaction. Examples of such solutes are noble gases and osmium tetroxide.[1]

Other examples

An old method of gold mining involves the absorption of gold into mercury.
A more current use of this word in is reference to spectrophotometry where the amount of light absorbed by a chemical bond is measured.[1]


  1. ^ a b c d McMurry, John (2003). Fundamentals of Organic Chemistry (Fifth ed.). Agnus McDonald. pp. 409. ISBN 0534395732. 

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