fe oh 2

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Iron(II) hydroxide
IUPAC name

Iron(II) hydroxide

Other names

Ferrous hydroxide, green rust


CAS Number

  • 18624-44-7 check

3D model (JSmol)

  • Interactive image
  • 8305416 check
ECHA InfoCard 100.038.581 Edit this at Wikidata

PubChem CID

  • 10129897
  • 7JIM5W32UU check

CompTox Dashboard (EPA)

  • DTXSID8066393 Edit this at Wikidata


  • InChI=1S/Fe.2H2O/h;2*1H2/q+2;;/p-2 check


  • InChI=1/Fe.2H2O/h;2*1H2/q+2;;/p-2



  • O[Fe]O


Chemical formula

Molar mass 89.86 g/mol
Appearance green solid
Density 3.4 g/cm3 [1]

Solubility in water

0.000052 g/100 g water (20 °C, pH 7)[2]

Solubility product (Ksp)

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8.0 x 10−16[3]
Flash point Non-flammable
Related compounds

Related compounds

Iron(II) oxide
Iron(III) hydroxide

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

Iron(II) hydroxide or ferrous hydroxide is an inorganic compound with the formula Fe(OH)2. It is produced when iron(II) salts, from a compound such as iron(II) sulfate, are treated with hydroxide ions. Iron(II) hydroxide is a white solid, but even traces of oxygen impart a greenish tinge. The air-oxidised solid is sometimes known as "green rust".

Preparation and reactions[edit]

Iron(II) hydroxide is poorly soluble in water (1.43 × 10−3 g/L), or 1.59 × 10−5 mol/L. It precipitates from the reaction of iron(II) and hydroxide salts:[4]

FeSO4 + 2 NaOH → Fe(OH)2 + Na2SO4

If the solution is not deoxygenated and iron not totally reduced in Fe(II), the precipitate can vary in colour starting from green đồ sộ reddish brown depending on the iron(III) nội dung. Iron(II) ions are easily substituted by iron(III) ions produced by its progressive oxidation.

It is also easily formed as a by-product of other reactions, a.o., in the synthesis of siderite, an iron carbonate (FeCO3), if the crystal growth conditions are imperfectly controlled.


Fe(OH)2 is a layer double hydroxide (LDH) easily accommodating in its crystal lattice ferric ions (Fe3+
) produced by oxidation of ferrous ions (Fe2+
) by the atmospheric oxygen (O2).


Green rust is a recently discovered mineralogical sườn. All forms of green rust (including fougerite) are more complex and variable than vãn the ideal iron(II) hydroxide compound.


Under anaerobic conditions, the iron(II) hydroxide can be oxidised by the protons of water đồ sộ sườn magnetite (iron(II,III) oxide) and molecular hydrogen. This process is described by the Schikorr reaction:

3 Fe(OH)2 → Fe3O4 + H2 + 2 H2O

Anions such as selenite and selenate can be easily adsorbed on the positively charged surface of iron(II) hydroxide, where they are subsequently reduced by Fe2+. The resulting products are poorly soluble (Se0, FeSe, or FeSe2).

Natural occurrence[edit]

Iron III hydroxide staining caused by oxidation of dissolved iron II and precipitation, Perth, Western nước Australia.

Iron dissolved in groundwater is in the reduced iron II sườn. If this groundwater comes in liên hệ with oxygen at the surface, e.g. in natural springs, iron II is oxidised đồ sộ iron III and forms insoluble hydroxides in water.[5] The natural analogue of iron(II) hydroxide compound is the very rare mineral amakinite, (Fe,Mg)(OH)2.[6][7]


Iron(II) hydroxide has also been investigated as an agent for the removal of toxic selenate and selenite ions from water systems such as wetlands. The iron(II) hydroxide reduces these ions đồ sộ elemental selenium, which is insoluble in water and precipitates out.[8]

In a basic solution iron(II) hydroxide is the electrochemically active material of the negative electrode of the nickel-iron battery.

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See also[edit]

  • Layered double hydroxides


  1. ^ Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3.
  2. ^ CRC Handbook of Chemistry and Physics, 84th Edition, CRC Press, 2004, pg 4-62
  3. ^ Stumm, Werner; Lee, G. F. (February 1961). "Oxygenation of Ferrous Iron" (PDF). Industrial & Engineering Chemistry. 53 (2): 143–146. doi:10.1021/ie50614a030. Retrieved 17 November 2022.
  4. ^ H. Lux "Iron(II) Hydroxide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1498.
  5. ^ lenntech.com
  6. ^ "Amakinite".
  7. ^ "List of Minerals". 21 March 2011.
  8. ^ Zingaro, Ralph A.; et al. (1997). "Reduction of oxoselenium anions by iron(II) hydroxide". Environment International. 23 (3): 299–304. doi:10.1016/S0160-4120(97)00032-9.