Iron(II) hydroxide
chemical compound
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
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:
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 to reddish brown depending on the iron(III) content. 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.
Structure
Fe(OH)2 adopts the brucite structure, i.e. the arrangement of the atoms in the crystal are the same as the arrangement of the atoms in Mg(OH)2. The Fe(II) centers are bonded to six hydroxide ligands.
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