Hydroxide
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In [[chemistry]], '''hydroxide''' is the most common name for the [[Diatomic molecule|diatomic]] [[anion]] OH<sup>−</sup>, consisting of [[oxygen]] and [[hydrogen]] [[atom]]s, usually derived from the [[Dissociation (chemistry)|dissociation]] of a [[base (chemistry)|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:
*[[Sodium hydroxide]] (NaOH)
*[[Potassium hydroxide]] (KOH)
*[[Calcium hydroxide]] (Ca(OH)<sub>2</sub>)
==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]], NH<sub>3</sub>:
NH<sub>3</sub>(g) + H<sub>2</sub>O(l) {{unicode|⇌}} [[ammonium|NH<sub>4</sub><sup>+</sup>]](aq) + OH<sup>−</sup>(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 [[Strong salts|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<sup>−</sup>[[Aqueous|(aq)]] + [[hydronium|H<sup>+</sup>]](aq) → [[water (molecule)|H<sub>2</sub>O]][[liquid|(l)]]
by omitting [[spectator ion]]s.
==Solubility==
Most inorganic hydroxide salts are [[insoluble]] in water, except for those with cations from [[Alkaline metal|Group I]], [[Ammonium|NH<sub>4</sub><sup>+</sup>]], [[Barium|Ba<sup>2+</sup>]], [[Strontium|Sr<sup>2+</sup>]], [[Calcium|Ca<sup>2+</sup>]] (little) or [[Thallium|Tl<sup>+</sup>]].
==Applications==
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]] and [[limonite]] have been used as low grade ''brown'' [[iron ore]]. The [[aluminium]] ore [[bauxite]] is composed largely of aluminium hydroxides.
==Ligand==
The hydroxide ion is a kind of [[ligand]]. It donates [[lone pair]]s of electrons, behaving as a [[Lewis base]]. Examples of complexes containing such a ligand include the aluminate ion [Al(OH)<sub>4</sub>]<sup>−</sup> and aurate ion [Au(OH)<sub>4</sub>]<sup>−</sup>.
==See also==
{{Wiktionary}}
*[[Hydronium]]
*[[Oxide]]
*[[Hydroxyl]]
*[[Hydroxy]]
==Notes==
* [http://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/j100016a003 Solvation and Transport of H<sub>3</sub>O<sup>+</sup> and OH<sup>−</sup> Ions in Water (JCP 99, 5749 (1995)]
<references/>
[[Category:Hydroxides| ]]
[[Category:Bases]]
[[Category:Oxoanions]]
[[Category:Water chemistry]]
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