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. When a Bronsted-Lowry acid is put in water, a covalent bond between an electronegative atom and a hydrogen atom is broken by heterolytic fission, which gives a proton and a negative ion. Dissociation is the opposite of association and recombination. The process is frequently confused with ionization.

Dissociation constant[edit | edit source]

For reversible dissociations in a chemical equilibrium

<math> AB \leftrightarrow a + b </math>

the dissociation constant K_d is the ratio of dissociated to undissociated compound

Salts[edit | edit source]

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[edit | edit source]

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 pK_a value).

Fragmentation[edit | edit source]

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

Receptors[edit | edit source]

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 pK_d value).