Iron(II) hydroxide: Difference between revisions

| verifiedrevid = 401606455

| Name = Iron(II) hydroxide

| ImageFile = Hydroxid železnatý.PNG

| ImageName = Iron(II) hydroxide

| IUPACName = Iron(II) hydroxide

| OtherNames = Ferrous hydroxide

| Section1 = {{Chembox Identifiers

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| SMILES = [Fe+2].[OH-].[OH-]

| CASNo_Ref = {{cascite|correct|CAS}}

| PubChem = 10129897

| Section2 = {{Chembox Properties

| Formula = Fe(OH)₂

| MolarMass = 89.86 g/mol

| Appearance = brown solid

| Density = 3.4 g/cm³ <ref>Pradyot Patnaik. ''Handbook of Inorganic Chemicals''. McGraw-Hill, 2002, ISBN 0070494398</ref>

| Solubility = 0.00015 g/100 mL (20 °C)

| SolubilityProduct = 8.0 x 10^-16

| MeltingPt =

| BoilingPt =

| Section3 = {{Chembox Hazards

| ExternalMSDS =

| EUIndex = Not listed

| MainHazards =

| RPhrases =

| SPhrases =

| FlashPt = Non-flammable

| Section8 = {{Chembox Related

| OtherCpds = [[Iron(II) oxide]]<br/>[[Iron(III) hydroxide]]

[[File:DSC01968 - Fe (II) Reactions.JPG|thumb|left|The second tube from the left has almost pure whitish iron(II) hydroxide.]]

[[File:Ferrous hydroxide.JPG|thumb|left|This container has a precipitate of dark greenish iron(II) hydroxide in it.]]

'''Iron(II) hydroxide''' or '''ferrous hydroxide''' is a [[Chemical compound|compound]] produced when iron(II) ions, from a compound such as [[iron(II) sulfate]], react with [[hydroxide]] ions. Iron(II) hydroxide itself is practically white, but even traces of oxygen impart it with a greenish tinge. If the solution was not deoxygenated and the iron reduced, the precipitate can vary in color starting from green to reddish brown depending on the iron(III) content. This precipitate is also known as "green rust" in the crystal lattice of which iron(II) ions are easily substituted by iron(III) ions produced by its progressive oxidation. In the presence of oxygen the color changes quickly. Green rust is a powerful reducing agent and also a [[Layered double hydroxides|layer double hydroxide]] (LDH) capable to sorb anions because of the presence of positive electrical charges borne on its surface. The mineralogical form of green rust is a recently discovered [[fougerite]]. All forms of green rust (including fougerite) are more complex and variable than the ideal iron(II) hydroxide compound. The natural analogue of iron(II) hydroxide compound is a very rare mineral [[amakinite]], (Fe,Mg)(OH)₂.

Iron(II) hydroxide is poorly soluble (1.43 &times; 10^&minus;3 [[gram|g]]/[[liter|L]]). It precipitates from the reaction of iron(II) sulfate and hydroxide ions (from a soluble compound containing hydroxide ion):

:FeSO₄ + 2 OH⁻ → Fe(OH)₂ + SO₄²⁻

It is also easily formed as an undesirable by-product of other reactions, a.o., in the synthesis of [[siderite]], an iron carbonate (FeCO₃), if the crystal growth conditions are poorly controlled (reagent concentrations, addition rate, addition order, pH, pCO₂, T, aging time, ...).

==Ageing and transformation into magnetite==

Under anaerobic conditions, the iron(II) hydroxide can be oxidized by the protons of water to form iron(II,III) oxide and molecular [[hydrogen]].

This process is described by the [[Schikorr reaction]]:

:3 Fe(OH)₂ → Fe₃O₄ + H₂ + 2 H₂O

The well crystallized iron(II,III) oxide (Fe₃O₄) is thermodynamically more stable than the iron(II) hydroxide.

==Uses==

Anions such as [[Selenite (ion)|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).

Iron(II) hydroxide has also been investigated as an agent for the removal of toxic [[selenate]] and [[selenous acid|selenite]] ions from water systems such as [[wetland]]s. The iron(II) hydroxide [[redox|reduces]] these ions to elemental [[selenium]], which is insoluble in water and [[precipitation (chemistry)|precipitates]] out.<ref>{{cite journal

| last = Zingaro

| first = Ralph A.

| coauthors = ''et al.''

| year = 1997

| title = Reduction of oxoselenium anions by iron(II) hydroxide

| journal = Environment International

| volume = 23

| issue = 3

| pages = 299–304

| doi = 10.1016/S0160-4120(97)00032-9

}}</ref>

Note: pK_sp = 15.097 where p is the -log and K_sp is the Solubility Product Constant. This means it has a low tendency to dissolve, but is not entirely insoluble. An acidic solution would allow this to disassociate more because the H⁺ would react with the OH^- in the compound.

* [[Rust]]

* [[Periodic table]]

[[Category:Inorganic compounds]]

[[Category:Iron compounds]]

[[ar:هيدروكسيد الحديد الثنائي]]

[[hu:Vas(II)-hidroxid]]

[[nl:IJzer(II)hydroxide]]

[[no:Jernhydroksid]]

[[pt:Hidróxido de ferro (II)]]

[[ru:Гидроксид железа(II)]]

[[simple:Iron(II) hydroxide]]

[[sv:Järn(II)hydroxid]]

[[zh:氢氧化亚铁]]