Iron(II) sulfate
Other names Ferrous sulfate; green vitriol; iron vitriol; copperas; melanterite; szomolnokite
Identifiers
CAS number	7720-78-7 Y,  17375-41-6 (monohydrate), 7782-63-0 (heptahydrate)
PubChem	24393
ChemSpider	22804 Y
UNII	RIB00980VW Y
EC number	231-753-5
ChEMBL	CHEMBL1200830 N
RTECS number	NO8500000
ATC code	B03AA07
Jmol-3D images	Image 1
SMILES [O-]S(=O)(=O)[O-].[Fe+2]
InChI InChI=1S/Fe.H2O4S/c;1-5(2,3)4/h;(H2,1,2,3,4)/q+2;/p-2 Y Key: BAUYGSIQEAFULO-UHFFFAOYSA-L Y InChI=1/Fe.H2O4S/c;1-5(2,3)4/h;(H2,1,2,3,4)/q+2;/p-2 Key: BAUYGSIQEAFULO-NUQVWONBAS
Properties
Molecular formula	FeSO4
Molar mass	151.908 g/mol (anhydrous) 169.92 g/mol (monohydrate) 278.05 g/mol (heptahydrate)
Appearance	blue/green or white crystals
Odor	odorless
Density	2.84 g/cm3 (anhydrous) 2.2 g/cm3 (pentahydrate) 1.898 g/cm3 (heptahydrate)
Melting point	70 °C (dehydration of heptahydrate) 400 °C (decomp)
Solubility in water	25.6 g/100mL (anhydrous) 48.6 g/100 mL (heptahydrate) (50 °C)
Solubility	negligible in alcohol
Refractive index (nD)	1.536 (pentahydrate) 1.478 (heptahydrate)
Hazards
EU Index	026-003-00-7 (anhydrous) 026-003-01-4 (heptahydrate)
EU classification	Harmful (Xn) Irritant (Xi)
R-phrases	R22, R36/38
S-phrases	(S2), S46
NFPA 704	0 1 0
Flash point	Non-flammable
Thermochemistry
Std enthalpy of formation ΔfHo298	−929 kJ·mol−1[1]
Standard molar entropy So298	121 J·mol−1·K−1[1]
Related compounds
Related compounds	Iron(III) sulfate
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Iron(II) sulfate (Br.E. iron(II) sulphate) or ferrous sulfate is the chemical compound with the formula FeSO₄. Known since ancient times as copperas and as green vitriol, the blue-green heptahydrate is the most common form of this material. All iron sulfates dissolve in water to give the same aquo complex [Fe(H₂O)₆]²⁺, which has octahedral molecular geometry and is paramagnetic.

Hydrates[link]

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)

At 90 °C, the heptahydrate loses water to form the colorless monohydrate. In its anhydrous, crystalline state, its standard enthalpy of formation is Δ_fH°_solid = -928.4 kJ·mol⁻¹ and its standard molar entropy is S°_solid = 107.5 J·K⁻¹·mol⁻¹. All mentioned mineral forms are connected with oxidation zones of Fe-bearing ore beds (pyrite, marcasite, chalcopyrite, etc.) and related environments (like coal fire sites). Many undergo rapid dehydration and sometimes oxidation.

Production and reactions[link]

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.^[2]

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

Reactions[link]

On heating, iron(II) sulfate first loses its water of crystallization and the original green crystals are converted into a dirty-yellow 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 480 °C.

2 FeSO₄ → Fe₂O₃ + SO₂ + SO₃

Like all iron(II) salts, iron(II) sulfate is a reducing agent. For example, it reduces nitric acid to nitrogen oxide and chlorine to chloride:

6 FeSO₄ + 3 H₂SO₄ + 2 HNO₃ → 3 Fe₂(SO₄)₃ + 4 H₂O + 2 NO

6 FeSO₄ + 3 Cl₂ → 2 Fe₂(SO₄)₃ + 2 FeCl₃

Ferrous sulfate outside titanium dioxide factory in Kaanaa, Pori.

Upon exposure to air, it oxidizes to form a corrosive brown-yellow coating of basic ferric sulfate, which is an adduct of ferric oxide and ferric sulfate:

12 FeSO₄ + 3 O₂ → 4 Fe₂(SO₄)₃ + 2 Fe₂O₃

Uses[link]

Industrially, ferrous sulfate is mainly used as a precursor to other iron compounds. It is a reducing agent, mostly for the reduction of chromate in cement.

Nutritional supplement[link]

Together with other iron compounds, ferrous sulfate is used to fortify foods and to treat 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.

Colorant[link]

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. 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.^[3]

Woodworkers use ferrous sulfate solutions to color maple wood a silvery hue.

Other uses[link]

In horticulture it is used for treating iron chlorosis.^[4] Although not as rapid-acting as iron chelate, its effects are longer-lasting. It can be mixed with compost and dug into to the soil to create a store which can last for years.^[5] It is also used as a lawn conditioner,^[5] and moss killer.

In the second half of the 19th century, ferrous sulfate was also used as a photographic developer for collodion process images.

Ferrous sulfate is sometimes added to the cooling water flowing through the brass tubes of a turbine condenser. It forms a corrosion-resistant, protective coating on the inside of the tube.

It is used as a gold refining chemical to precipitate metallic gold from auric chloride solutions (gold that has been dissolved into solution with aqua regia).

It has been applied for the purification of water by flocculation and for phosphate removal in municipal and industrial sewage treatment plants to prevent eutrophication of surface water bodies.^{[citation needed]}

It is used as a traditional method of treating wood panel on houses, either alone, dissolved in water, or as a component of water-based paint.

Green vitriol is also a useful reagent in the identification of mushrooms.^[6]

See also[link]

• Iron(III) sulfate, the other common simple sulfate of iron.
• Mohr's salt (Ammonium iron(II) sulfate), a common double salt of ammonium sulfate with iron(II) sulfate.

References[link]

External links[link]

Wikimedia Commons has media related to: Iron(II) sulfate