DISSOCIATION (CHEMISTRY)

'Dissociation' in chemistry and biochemistry is a general process in which ionic compounds (complexes, molecules, or salts) separate or split into smaller molecules, ions, or radicals, usually in a reversible manner. Dissociation is the opposite of 'association' and 'recombination'. The process is frequently confused with ionization.

Contents

Dissociation constant

Salts

Acids

Fragmentation

Receptors

Dissociation constant

For reversible dissociations in a chemical equilibrium
: $AB\; leftrightarrow\; a\; +\; b$
the dissociation constant ''K''_d is the ratio of dissociated to undissociated compound
:

Salts

The dissociation of salts by solvation in a solution like water means the separation of the anions and cations. The salt can be recovered by evaporation of the solvent. See also: Solubility equilibrium

Acids

The dissociation of acids in a solution means the split-off of a proton H⁺, see Acid-base reaction theories. This is an equilibrium process, meaning that dissociation and recombination takes place at the same time. The acid dissociation constant ''K''_a is an indicator of the acid strength: stronger acids have a higher ''K''_a value (and a lower p''K''_a value).

Fragmentation

Fragmentation of a molecule can take place by a process of heterolysis or homolysis.

Receptors

Receptors are proteins that bind small ligands. The dissociation constant ''K''_d is used as indicator of the affinity of the ligand to the receptor. The higher the affinity of the ligand for the receptor the lower the ''K''_d value (and the higher the p''K''_d value).