In chemistry, hydroxide is the most common name for the diatomic anion OH−, consisting of oxygen and hydrogen atoms, usually derived from the dissociation of a base. It is one of the simplest diatomic ions known.
Inorganic compounds that contain the hydroxyl group are referred to as hydroxides. Common hydroxides include:
Hydroxide as a base
Most compounds containing hydroxide are bases.
An Arrhenius base is a substance that produces hydroxide ions when dissolved in aqueous solution. One example would be ammonia, NH3:
NH3(g) + H2O(l) ⇌ NH4+(aq) + OH−(aq)
Thus, hydroxide ions are heavily involved in acid-base reactions as well as the special double displacement reaction called neutralization.
Salts containing hydroxide are called base salts. Base salts will dissociate into a cation and one or more hydroxide ions in water, making the solution basic. Base salts will undergo neutralisation reactions with acids. In general acid-alkali reactions can be simplified to
- OH−(aq) + H+(aq) → H2O(l)
by omitting spectator ions.
Most inorganic hydroxide salts are insoluble in water, except for those with cations from Group I, NH4+, Ba2+, Sr2+, Ca2+ (little) or Tl+.
Hydroxides and hydroxide ions are relatively common. Many useful chemicals and chemical processes involve hydroxides or hydroxide ions. Sodium hydroxide
(lye) is used in industry as a strong base, potassium hydroxide
is used in agriculture, and iron hydroxide
minerals such as goethite
have been used as low grade brown iron ore
. The aluminium
is composed largely of aluminium hydroxides.
The hydroxide ion is a kind of ligand
. It donates lone pairs
of electrons, behaving as a Lewis base
. Examples of complexes containing such a ligand include the aluminate ion [Al(OH)4
and aurate ion [Au(OH)4