Editing Iron(III) oxide (section)

==Hydrated iron(III) oxides==
Several hydrates of Iron(III) oxide exist.
When alkali is added to solutions of soluble Fe(III) salts, a red-brown gelatinous precipitate forms. This is ''not'' {{chem2|Fe(OH)3}}, but {{chem2|Fe2O3*H2O}} (also written as {{chem2|Fe(O)OH}}).

Several forms of the hydrated oxide of Fe(III) exist as well. The red [[lepidocrocite]] (γ-{{chem2|Fe(O)OH}}) occurs on the outside of [[rusticle]]s, and the orange [[goethite]] (α-{{chem2|Fe(O)OH}}) occurs internally in rusticles.
When {{chem2|Fe2O3}}·H<sub>2</sub>O is heated, it loses its water of hydration. Further heating at {{val|1670|u=K}} converts {{chem2|Fe2O3}} to black {{chem2|Fe3O4}} ({{chem2|Fe^{II}Fe^{III}2O4}}), which is known as the mineral [[magnetite]].

{{chem2|Fe(O)OH}} is soluble in acids, giving {{chem2|[Fe(H2O)6](3+)}}. In concentrated aqueous alkali, {{chem2|Fe2O3}} gives {{chem2|[Fe(OH)6](3-)}}.<ref name="InorgChem">{{cite book|title = Inorganic Chemistry|url = https://archive.org/details/inorganicchemist00hous_159|url-access = limited|edition = 3rd|chapter = Chapter 22: ''d''-block metal chemistry: the first row elements|first1 = Catherine E.|last1 = Housecroft|first2 = Alan G.|last2 = Sharpe|publisher = Pearson|year = 2008|isbn = 978-0-13-175553-6|page = [https://archive.org/details/inorganicchemist00hous_159/page/n754 716]}}</ref>