Iron(III) oxide-hydroxide
Samples of iron(III) oxide-hydroxide monohydrate in a vial, and a spoon | |
Names | |
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IUPAC name
Iron(III) oxide-hydroxide
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Other names
Ferric acid
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Identifiers | |
1310-14-1 ![]() 20344-49-4 ![]() |
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ChemSpider | 82623 ![]() |
EC Number | 215-176-6 |
Jmol 3D model | Interactive image |
MeSH | Goethite |
PubChem | 91502 |
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Properties | |
Appearance | Vivid, dark orange, opaque crystals |
Odor | odorless |
Density | 4.25 g/cm3 |
insoluble at pH 7 | |
Solubility product (Ksp)
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2.79×10−39 for Fe(OH)3[1] |
Vapor pressure | {{{value}}} |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references | |
A number of chemicals are dubbed iron(III) oxide-hydroxide. These chemicals are oxide-hydroxides of iron, and may occur in anhydrous (FeO(OH)) or hydrated (FeO(OH)·nH2O) forms. The monohydrate (FeO(OH)·H2O) might otherwise be described as iron(III) hydroxide (Fe(OH)3), and is also known as hydrated iron oxide or yellow iron oxide.
Contents
Natural occurrences
Iron(III) oxide-hydroxide occurs naturally as four minerals, the polymorphs denoted by the Greek letters α, β, γ and δ: Goethite, α-FeO(OH), has been used as a pigment since prehistoric times. Akaganéite is the β polymorph, formed by weathering and noted for its presence in some meteorhe 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 - 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
Yellow iron oxide (CAS
Chemistry
In a solution containing both iron(II) and iron(III), ferric hydroxide precipitates between pH 2 to 4:[citation needed]
- Fe3+ + 3OH− → Fe(OH)3
Ferrous hydroxide precipitates between pH 7 to 9:[citation needed]
- Fe2+ + 2OH− → Fe(OH)2
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:
- FeCl3 + 3NaOH → Fe(OH)3 + 3NaCl
Alternately iron(II) may be oxidized to iron(III) by hydrogen peroxide in the presence of an acid:
- Fe2+ → Fe3+ + e−
- H2O2 + 2 e− → 2 OH−
Overall equation:
- 2 Fe2+ + H2O2 + 2 H+ → 2 Fe3+ + 2 H2O
Safety
The risk and safety phrases for iron oxides are R36, R37, R38, S26, and S36.
See also
References
- ↑ http://bilbo.chm.uri.edu/CHM112/tables/KspTable.htm
- ↑ Iron Oxide Hydroxide (GFO) Phosphate Binders
- ↑ 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)
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