Editing Hydroxide (section)

===Boron group elements===
[[File:AlHydrolysis.png|thumb|Aluminium hydrolysis as a function of pH. Water molecules attached to Al are omitted]]
The simplest hydroxide of boron B(OH)<sub>3</sub>, known as [[boric acid]], is an acid. Unlike the hydroxides of the alkali and alkaline earth hydroxides, it does not dissociate in aqueous solution. Instead, it reacts with water molecules acting as a Lewis acid, releasing protons.
:B(OH)<sub>3</sub> + H<sub>2</sub>O {{eqm}} [[tetrahydroxyborate|{{chem|B(OH)|4|−}}]] + H<sup>+</sup>
A variety of [[oxyanion]]s of boron are known, which, in the protonated form, contain hydroxide groups.<ref>Housectroft, p.&nbsp;263</ref>
[[File:Tetrahydroxoaluminate ion.svg|thumb|100px|left|Tetrahydroxo-<br>aluminate(III) ion]]
[[Aluminium hydroxide]] Al(OH)<sub>3</sub> is amphoteric and dissolves in alkaline solution.<ref name=amph/>
:Al(OH)<sub>3</sub> (solid) + OH<sup>−</sup>&nbsp;(aq) {{eqm}} [[aluminate|{{chem|Al(OH)|4|−}}]]&nbsp;(aq)
In the [[Bayer process]]<ref>[http://www.world-aluminium.org/?pg=85 Bayer process chemistry]</ref> for the production of pure aluminium oxide from [[bauxite]] minerals this equilibrium is manipulated by careful control of temperature and alkali concentration. In the first phase, aluminium dissolves in hot alkaline solution as {{chem|Al(OH)|4|−}}, but other hydroxides usually present in the mineral, such as iron hydroxides, do not dissolve because they are not amphoteric. After removal of the insolubles, the so-called [[red mud]], pure aluminium hydroxide is made to precipitate by reducing the temperature and adding water to the extract, which, by diluting the alkali, lowers the pH of the solution. Basic aluminium hydroxide AlO(OH), which may be present in bauxite, is also amphoteric.

In mildly acidic solutions, the hydroxo/hydroxido complexes formed by aluminium are somewhat different from those of boron, reflecting the greater size of Al(III) vs. B(III). The concentration of the species [Al<sub>13</sub>(OH)<sub>32</sub>]<sup>7+</sup> is very dependent on the total aluminium concentration. Various other hydroxo complexes are found in crystalline compounds. Perhaps the most important is the basic hydroxide AlO(OH), a polymeric material known by the names of the mineral forms [[boehmite]] or [[diaspore]], depending on crystal structure. [[Gallium hydroxide]],<ref name=amph/> [[indium hydroxide]], and [[thallium(III) hydroxide]] are also amphoteric. [[Thallium(I) hydroxide]] is a strong base.<ref>James E. House [https://books.google.com/books?id=ocKWuxOur-kC&pg=PA764 Inorganic chemistry], Academic Press, 2008, {{ISBN|0-12-356786-6}}, p.&nbsp;764</ref>