Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula FeSO4·xH2O. These compounds exist most commonly as the heptahydrate (x = 7) but are known for several values of x. The hydrated form is used medically to treat iron deficiency, and also for industrial applications. Known since ancient times as copperas and as green vitriol (vitriol is an archaic name for sulfate), the blue-green heptahydrate (hydrate with 7 molecules of water) is the most common form of this material. All the iron(II) sulfates dissolve in water to give the same aquo complex [Fe(H2O)6]2+, which has octahedral molecular geometry and is paramagnetic. The name copperas dates from times when the copper(II) sulfate was known as blue copperas, and perhaps in analogy, iron(II) and zinc sulfate were known respectively as green and white copperas.
Iron(II) sulfate when dissolved in water
Iron(II) sulphate; Ferrous sulfate, Green vitriol, Iron vitriol, Copperas, Melanterite, Szomolnokite
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||151.91 g/mol (anhydrous)|
169.93 g/mol (monohydrate)
241.99 g/mol (pentahydrate)
260.00 g/mol (hexahydrate)
278.02 g/mol (heptahydrate)
|Appearance||White crystals (anhydrous)|
White-yellow crystals (monohydrate)
Blue-green crystals (heptahydrate)
|Density||3.65 g/cm3 (anhydrous)|
3 g/cm3 (monohydrate)
2.15 g/cm3 (pentahydrate)
1.934 g/cm3 (hexahydrate)
1.895 g/cm3 (heptahydrate)
|Melting point|| 680 °C (1,256 °F; 953 K) |
300 °C (572 °F; 573 K)
60–64 °C (140–147 °F; 333–337 K)
44.69 g/100 mL (77 °C)
35.97 g/100 mL (90.1 °C)
15.65 g/100 mL (0 °C)
20.5 g/100 mL (10 °C)
29.51 g/100 mL (25 °C)
39.89 g/100 mL (40.1 °C)
51.35 g/100 mL (54 °C)
|Solubility||Negligible in alcohol|
|Solubility in ethylene glycol||6.4 g/100 g (20 °C)|
|Vapor pressure||1.95 kPa (heptahydrate)|
|1.24×10−2 cm3/mol (anhydrous)|
1.05×10−2 cm3/mol (monohydrate)
1.12×10−2 cm3/mol (heptahydrate)
Refractive index (nD)
1.526–1.528 (21 °C, tetrahydrate)
|Orthorhombic, oP24 (anhydrous)|
Monoclinic, mS36 (monohydrate)
Monoclinic, mP72 (tetrahydrate)
Triclinic, aP42 (pentahydrate)
Monoclinic, mS192 (hexahydrate)
Monoclinic, mP108 (heptahydrate)
|Pnma, No. 62 (anhydrous) |
C2/c, No. 15 (monohydrate, hexahydrate)
P21/n, No. 14 (tetrahydrate)
P1, No. 2 (pentahydrate)
P21/c, No. 14 (heptahydrate)
|2/m 2/m 2/m (anhydrous)|
2/m (monohydrate, tetrahydrate, hexahydrate, heptahydrate)
a = 8.704(2) Å, b = 6.801(3) Å, c = 4.786(8) Å (293 K, anhydrous)
α = 90°, β = 90°, γ = 90°
Heat capacity (C)
|100.6 J/mol·K (anhydrous)|
394.5 J/mol·K (heptahydrate)
|107.5 J/mol·K (anhydrous)|
409.1 J/mol·K (heptahydrate)
Std enthalpy of
|−928.4 kJ/mol (anhydrous)|
−3016 kJ/mol (heptahydrate)
Gibbs free energy (ΔfG˚)
|−820.8 kJ/mol (anhydrous)|
−2512 kJ/mol (heptahydrate)
|GHS Signal word||Warning|
|H302, H315, H319|
|NFPA 704 (fire diamond)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|237 mg/kg (rat, oral)|
|NIOSH (US health exposure limits):|
|TWA 1 mg/m3|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system. In 2017, it was the 92nd most commonly prescribed medication in the United States, with more than eight million prescriptions.
Industrially, ferrous sulfate is mainly used as a precursor to other iron compounds. It is a reducing agent, and as such is useful for the reduction of chromate in cement to less toxic Cr(III) compounds. Historically ferrous sulfate was used in the textile industry for centuries as a dye fixative. It is used historically to blacken leather and as a constituent of ink. The preparation of sulfuric acid ('oil of vitriol') by the distillation of green vitriol (Iron(II) sulfate) has been known for at least 700 years.
Together with other iron compounds, ferrous sulfate is used to fortify foods and to treat and prevent iron deficiency anemia. Constipation is a frequent and uncomfortable side effect associated with the administration of oral iron supplements. Stool softeners often are prescribed to prevent constipation.
Ferrous sulfate was used in the manufacture of inks, most notably iron gall ink, which was used from the middle ages until the end of the eighteenth century. Chemical tests made on the Lachish letters (c.588–586 BCE) showed the possible presence of iron. It is thought that oak galls and copperas may have been used in making the ink on those letters. It also finds use in wool dyeing as a mordant. Harewood, a material used in marquetry and parquetry since the 17th century, is also made using ferrous sulfate.
Two different methods for the direct application of indigo dye were developed in England in the eighteenth century and remained in use well into the nineteenth century. One of these, known as china blue, involved iron(II) sulfate. After printing an insoluble form of indigo onto the fabric, the indigo was reduced to leuco-indigo in a sequence of baths of ferrous sulfate (with reoxidation to indigo in air between immersions). The china blue process could make sharp designs, but it could not produce the dark hues of other methods.
Sometimes, it is included in canned black olives as an artificial colorant.
Ferrous sulfate can also be used to stain concrete and some limestones and sandstones a yellowish rust color.
In horticulture it is used for treating iron chlorosis. Although not as rapid-acting as ferric EDTA, its effects are longer-lasting. It can be mixed with compost and dug into the soil to create a store which can last for years. It is also used as a lawn conditioner, and moss killer.
Ferrous sulfate is sometimes added to the cooling water flowing through the brass tubes of turbine condensers to form a corrosion-resistant protective coating.
It is used in gold refining to precipitate metallic gold from auric chloride solutions (gold dissolved in solution with aqua regia).
It has been used in the purification of water by flocculation and for phosphate removal in municipal and industrial sewage treatment plants to prevent eutrophication of surface water bodies.
Green vitriol is also a useful reagent in the identification of mushrooms.
It is used as the iron catalyst component of Fenton's reagent.
It is one of the key ingredients in iron gall ink.
Iron(II) sulfate can be found in various states of hydration, and several of these forms exist in nature.
- FeSO4·H2O (mineral: Szomolnokite, relatively rare)
- FeSO4·4H2O (mineral: Rozenite, white, relatively common, may be dehydratation product of melanterite)
- FeSO4·5H2O (mineral: Siderotil, relatively rare)
- FeSO4·6H2O (mineral: Ferrohexahydrite, relatively rare)
- FeSO4·7H2O (mineral: Melanterite, blue-green, relatively common)
The tetrahydrate is stabilized when the temperature of aqueous solutions reaches 56.6 °C (133.9 °F). At 64.8 °C (148.6 °F) these solutions form both the tetrahydrate and monohydrate.
All mentioned mineral forms are connected with oxidation zones of iron-bearing ore beds (pyrite, marcasite, chalcopyrite, etc.) and related environments (like coal fire sites). Many undergo rapid dehydration and sometimes oxidation.
Production and reactionsEdit
In the finishing of steel prior to plating or coating, the steel sheet or rod is passed through pickling baths of sulfuric acid. This treatment produces large quantities of iron(II) sulfate as a by-product.
- Fe + H2SO4 → FeSO4 + H2
Ferrous sulfate is also prepared commercially by oxidation of pyrite:
- 2 FeS2 + 7 O2 + 2 H2O → 2 FeSO4 + 2 H2SO4
It can be produced by displacement of metals less reactive than Iron from solutions of their sulfate: CuSO4 + Fe → FeSO4 + Cu
On heating, iron(II) sulfate first loses its water of crystallization and the original green crystals are converted into a white colored anhydrous solid. When further heated, the anhydrous material releases sulfur dioxide and white fumes of sulfur trioxide, leaving a reddish-brown iron(III) oxide. Decomposition of iron(II) sulfate begins at about 680 °C (1,256 °F).
- 2 FeSO4 → Fe2O3 + SO2 + SO3
- 6 FeSO4 + 3 H2SO4 + 2 HNO3 → 3 Fe2(SO4)3 + 4 H2O + 2 NO
- 6 FeSO4 + 3 Cl2 → 2 Fe2(SO4)3 + 2 FeCl3
- 12 FeSO4 + 3 O2 → 4 Fe2(SO4)3 + 2 Fe2O3
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- How To Stain Concrete with Iron Sulfate
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