View source for Ferric hydroxide

{{Chembox new
| Watchedfields = changed
| verifiedrevid = 477000862
| ImageFile = Iron III.png

|  ImageFile_Ref = {{chemboximage|correct|??}}
|  ImageSize = 244
|  ImageName = Samples of iron(III) oxide-hydroxide monohydrate in a vial, and a spoon
| IUPACName = Iron(III) oxide-hydroxide
| OtherNames = Ferric acid
| Section1 = {{Chembox Identifiers
|  CASNo = 1310-14-1
|   CASNo_Ref = {{cascite|correct|CAS}}
|  CASNo1 = 20344-49-4
|   CASNo1_Ref = {{cascite|correct|CAS}}
|  PubChem = 91502
|   PubChem_Ref = {{Pubchemcite|correct|PubChem}}
|  ChemSpiderID = 82623
|   ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|  EINECS = 215-176-6
|  MeSHName = Goethite
|  SMILES = [O][Fe]O
|  StdInChI = 1S/Fe.H2O.O/h;1H2;/q+1;;/p-1
|   StdInChI_Ref = {{stdinchicite|correct|chemspider}}
|  StdInChIKey = AEIXRCIKZIZYPM-UHFFFAOYSA-M
|   StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
}}
| Section2 = {{Chembox Properties
|  ExactMass = 88.85174 g mol<sup>−1</sup> <!-- Fe(OH)3 -->
|  Appearance = Vivid, dark orange, opaque crystals
|  Odor = odorless
|  Density = 4.25 g/cm<sup>3</sup>
|  Solubility = insoluble at pH 7
|  SolubilityProduct = 2.79×10<sup>−39</sup> for Fe(OH)<sub>3</sub><ref>http://bilbo.chm.uri.edu/CHM112/tables/KspTable.htm</ref>
}}
| Section3 = {{Chembox Hazards
|  NFPA-H = 1
|  NFPA-F = 0
|  NFPA-R = 0
}}
}}
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{{SI}}
{{CMG}}
== Overview ==
A number of chemicals are dubbed '''iron(III) oxide-hydroxide'''. These chemicals are [[oxide]]-[[hydroxide]]s of [[iron]], and may occur in [[anhydrous]] ({{Iron}}{{Oxygen}}({{Hydroxide}})) or [[hydrate]]d ({{Iron}}{{Oxygen}}({{Hydroxide}})·n[[Water|H<sub>2</sub>O]]) forms. The monohydrate
({{Iron}}{{Oxygen}}({{Hydroxide}})·[[Water|H<sub>2</sub>O]]) might otherwise be described as '''iron(III) hydroxide''' ({{Iron}}({{Hydroxide}})<sub>3</sub>), and is also known as '''hydrated iron oxide''' or '''yellow iron oxide'''.

==Natural occurrences ==
Iron(III) oxide-hydroxide occurs naturally as four [[mineral]]s, the polymorphs denoted by the Greek letters α, β, γ and δ: [[Goethite]], α-FeO(OH), has been used a pigment since prehistoric times. [[Akaganéite]] is the β polymorph, formed by weathering and noted for its presence in some meteorites and the lunar surface. The γ polymorph [[lepidocrocite]] is commonly encountered as [[rust]] on the inside of steel water pipes and tanks. [[Feroxyhyte]] (δ) is formed under the high pressure conditions of sea and ocean floors, being thermodynamically unstable with respect to the α polymorph (goethite) at surface conditions. It also occurs as siderogel - a colloid<!-- of the hydrate and not treated as mineral due to being amorphous--> - and [[limonite]], which is a commonly found mixture of mainly goethite, lepidocrocite, [[quartz]] and [[clay minerals]]. Goethite and lepidocrocite, both crystallizing in orthorhombic system, are the most common forms of iron(III) oxide-hydroxide and the most important mineral carriers of iron in soils. The mineral [[ferrihydrite]], also a soil constituent, is a related compound.

==Uses==
<!-- Move this to the appropriate mineral page -->
Yellow iron oxide (CAS {{CASREF|CAS=51274-00-1}}) is used as a [[pigment]], e.g. '''Pigment Yellow 42'''  or '''C.I. 77492'''. Pigment Yellow 42 is [[Food and Drug Administration]] (FDA) approved for use in [[cosmetics]] and is used in some [[tattoo]] inks. Solid material color ranges from yellow through dark-brown to black. Iron oxide-hydroxide is also used in [[aquarium]] water treatment as a [[phosphate]] binder.<ref>{{URL| http://www.reefkeeping.com/issues/2004-11/rhf/index.php |Iron Oxide Hydroxide (GFO) Phosphate Binders}}</ref>
also recently, two form of Iron oxide-hydroxides [[nanoparticle]]s are identified as very good [[adsorbent]]s for lead removal from aquatic media.<ref>{{URL| https://www.researchgate.net/publication/264488689_Iron_oxidehydroxide_%28-FeOOH%29_nanoparticles_as_high_potential_adsorbents_for_lead_removal_from_polluted_aquatic_media |Rahimi, Safoora, Rozita M. Moattari, Laleh Rajabi, Ali Ashraf Derakhshan, and Mohammad Keyhani. "Iron Oxide/hydroxide (α, γ-FeOOH) Nanoparticles as High Potential Adsorbents for Lead Removal from Polluted Aquatic Media." Journal of Industrial and Engineering Chemistry (2014)}}</ref>

==Chemistry==
In a solution containing both iron(II) and iron(III), ferric hydroxide precipitates between pH 2 to 4:{{Citation needed|date=April 2013}}
:Fe<sup>3+</sup> + 3OH<sup>−</sup> → Fe(OH)<sub>3</sub>
Ferrous hydroxide precipitates between pH 7 to 9:{{Citation needed|date=April 2013}}
:Fe<sup>2+</sup> + 2OH<sup>−</sup> → Fe(OH)<sub>2</sub>
This property of iron cations is exploited for the [[fractional precipitation]] of the two hydroxides in [[chemical analysis]].

==Production==
It is obtained by reacting ferric chloride with sodium hydroxide:
:FeCl<sub>3</sub> + 3NaOH → Fe(OH)<sub>3</sub> + 3NaCl

Alternately iron(II) may be oxidized to iron(III) by hydrogen peroxide in the presence of an acid:
:Fe<sup>2+</sup> → Fe<sup>3+</sup> + e<sup>−</sup>
:H<sub>2</sub>O<sub>2</sub> + 2 e<sup>−</sup> → 2 OH<sup>−</sup>
Overall equation:
:2 Fe<sup>2+</sup> + H<sub>2</sub>O<sub>2</sub> + 2 H<sup>+</sup> → 2 Fe<sup>3+</sup> + 2 H<sub>2</sub>O

==Safety==
The risk and [[safety phrase]]s for iron oxides are {{R36}}, {{R37}}, {{R38}}, {{S26}}, and {{S36}}.

==See also==
*[[Rust]]
*[[Iron oxide]]
*[[Iron pillar of Delhi]]

==References==
{{reflist|2}}

==External links==

{{Iron compounds}}

[[Category:drug]]
[[Category:Iron compounds]]
[[Category:Oxides]]
[[Category:Hydroxides]]


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