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)
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|
GHS hazard statements
|H302, H315, H319|
GHS precautionary statements
|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 2018, it was the 94th most commonly prescribed medication in the United States, with more than 8 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 iron gall 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.
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.
Pigment and craft
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 18th 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 18th century and remained in use well into the 19th 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.
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)
Mineral forms are found in oxidation zones of iron-bearing ore beds, e.g. pyrite, marcasite, chalcopyrite, etc. They are also found in related environments, like coal fire sites. Many rapidly dehydrate and sometimes oxidize. Numerous other, more complex (either basic, hydrated, and/or containing additional cations) Fe(II)-bearing sulfates exist in such environments, with copiapite being a common example.
Production and reactions
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
Another source of large amounts results from the production of titanium dioxide from ilmenite via the sulfate process.
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
Upon dissolving in water, ferrous sulfates form the metal aquo complex [Fe(H2O)6]2+, which is an almost colorless, paramagnetic ion.
On heating, iron(II) sulfate first loses its water of crystallization and the original green crystals are converted into a white anhydrous solid. When further heated, the anhydrous material releases sulfur dioxide, leaving a reddish-brown iron(III) oxide. Decomposition of iron(II) sulfate begins at about 680 °C (1,256 °F).
- 2 FeSO4 → Fe2O3 + 2 SO2 + O2
- 6 FeSO4 + 3 H2SO4 + 2 HNO3 → 3 Fe2(SO4)3 + 4 H2O + 2 NO
- 6 FeSO4 + 3 Cl2 → 2 Fe2(SO4)3 + 2 FeCl3
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|Wikimedia Commons has media related to Iron(II) sulfate.|
- "Ferrous sulfate". Drug Information Portal. U.S. National Library of Medicine.
- "Product Information". Chemical Land21. January 10, 2007.
- Hunt, T. Sterry (1879). . The American Cyclopædia.