Iron(II) sulfate

Iron(II) sulfate

Names
IUPAC name Iron(II) sulfate
Other names Ferrous sulfate, Green vitriol, Iron vitriol, Copperas, Melanterite, Szomolnokite
Identifiers
ATC code	B03AA07
CAS Registry Number	7720-78-7 (anhydrous) Y 17375-41-6 (monohydrate) N 7782-63-0 (heptahydrate) N
ChEBI	CHEBI:75832 N
ChEMBL	ChEMBL1200830 N
ChemSpider	22804 (anhydrous) Y 56459 (monohydrate) N 22804 (heptahydrate) N
EC-number	231-753-5
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
Jmol-3D images	Image
PubChem	24393 (anhydrous) 62712 (monohydrate) 62662 (heptahydrate)
RTECS number	NO8500000 (anhydrous) NO8510000 (heptahydrate)
SMILES [O-]S(=O)(=O)[O-].[Fe+2]
UNII	2IDP3X9OUD (anhydrous) N RIB00980VW (monohydrate) N G0Z5449449 (dihydrate) N 39R4TAN1VT (heptahydrate) N
UN number	3077
Properties
Molecular formula	FeO4S
Molar mass	151.91 g·mol−1
Appearance	White crystals (anhydrous) White-yellow crystals (monohydrate) Blue-green crystals (heptahydrate)
Odor	Odorless
Density	3.65 g/cm3 (anhydrous) 3 g/cm3 (monohydrate) 2.15 g/cm3 (pentahydrate)[1] 1.934 g/cm3 (hexahydrate)[2] 1.895 g/cm3 (heptahydrate)[3]
Melting point	680 °C (1,256 °F; 953 K) (anhydrous) decomposes[4] 300 °C (572 °F; 573 K) (monohydrate) decomposes 60–64 °C (140–147 °F; 333–337 K) (heptahydrate) decomposes[3][5]
Solubility in water	Monohydrate: 44.69 g/100 mL (77 °C) 35.97 g/100 mL (90.1 °C) Heptahydrate: 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)[6]
Solubility	Negligible in alcohol
Solubility in ethylene glycol	6.4 g/100 g (20 °C)[4]
Vapor pressure	1.95 kPa (heptahydrate)[7]
Magnetic susceptibility (χ)	1.24·10−2 cm3/mol (anhydrous) 1.05·10−2 cm3/mol (monohydrate) 1.12·10−2 cm3/mol (heptahydrate)[3]
Refractive index (nD)	1.591 (monohydrate)[8] 1.526–1.528 (21 °C, tetrahydrate)[9] 1.513–1.515 (pentahydrate)[1] 1.468 (hexahydrate)[2] 1.471 (heptahydrate)[10]
Structure
Crystal structure	Orthorhombic, oP24 (anhydrous)[11] Monoclinic, mS36 (monohydrate)[8] Monoclinic, mP72 (tetrahydrate)[9] Triclinic, aP42 (pentahydrate)[1] Monoclinic, mS192 (hexahydrate)[2] Monoclinic, mP108 (heptahydrate)[3][10]
Space group	Pnma, No. 62 (anhydrous) [11] C2/c, No. 15 (monohydrate, hexahydrate)[2][8] P21/n, No. 14 (tetrahydrate)[9] P1, No. 2 (pentahydrate)[1] P21/c, No. 14 (heptahydrate)[10]
Point group	2/m 2/m 2/m (anhydrous)[11] 2/m (monohydrate, tetrahydrate, hexahydrate, heptahydrate)[2][8][9][10] 1 (pentahydrate)[1]
Lattice constant	a = 8.704(2) Å, b = 6.801(3) Å, c = 4.786(8) Å (293 K, anhydrous)[11]
Lattice constant	α = 90°, β = 90°, γ = 90°
Coordination geometry	Octahedral (Fe2+)
Thermochemistry
Specific heat capacity (C)	100.6 J/mol·K (anhydrous)[3] 394.5 J/mol·K (heptahydrate)[12]
Std molar entropy (So298)	107.5 J/mol·K (anhydrous)[3] 409.1 J/mol·K (heptahydrate)[12]
Std enthalpy of formation (ΔfHo298)	−928.4 kJ/mol (anhydrous)[3] −3016 kJ/mol (heptahydrate)[12]
Gibbs free energy (ΔfG˚)	−820.8 kJ/mol (anhydrous)[3] −2512 kJ/mol (heptahydrate)[12]
Hazards
GHS pictograms	[7]
GHS signal word	Warning
GHS hazard statements	H302, H315, H319[7]
GHS precautionary statements	P305+351+338[7]
EU Index	026-003-00-7 (anhydrous) 026-003-01-4 (heptahydrate)
EU classification	Xi Xn
R-phrases	R22, R36/38
S-phrases	(S2), S46
NFPA 704	1 2 1
LD50 (Median lethal dose)	237 mg/kg (rat, oral)[5]
US health exposure limits (NIOSH):
REL (Recommended)	TWA 1 mg/m3[13]
Related compounds
Other cations	Cobalt(II) sulfate Copper(II) sulfate Manganese(II) sulfate Nickel(II) sulfate
Related compounds	Iron(III) sulfate
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
N verify (what is: Y/N?)
Infobox references

Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate is a salt with the formula FeSO₄. It is used medically to treat iron deficiency, and also for industrial applications. 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

Iron(II) sulfate can be found in various states of hydration, and several of these forms exist in nature.

• FeSO₄·H₂O (mineral: Szomolnokite,^[8] relatively rare)
• FeSO₄·4H₂O (mineral: Rozenite,^[9] white, relatively common, may be dehydratation product of melanterite)
• FeSO₄·5H₂O (mineral: Siderotil,^[1] relatively rare)
• FeSO₄·6H₂O (mineral: Ferrohexahydrite,^[2] relatively rare)
• FeSO₄·7H₂O (mineral: Melanterite,^[10] blue-green, relatively common)

Iron(II) sulfate heptahydrate, Melanterite (FeSO₄·7H₂O)

The heptahydrate in solution (water as solvent) transforms to both heptahydrate and tetrahydrate when the temperature reaches 56.6 °C (133.9 °F). Then at 64.8 °C (148.6 °F) they form both tetrahydrate and monohydrate.^[6]

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.

Iron(II) sulfate tetrahydrate, Rozenite (FeSO₄·4H₂O)

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.^[14]

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

On heating, iron(II) sulfate first loses its water of crystallization and the original green crystals are converted into a brown 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

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

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

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

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 [circa 588/6 BCE] showed the possible presence of iron (Torczyner, Lachish Letters, pp. 188–95). It is thought that oak galls and copperas may have been used in making the ink on those letters.^[15] 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.^[16]

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

Other uses

In horticulture it is used for treating iron chlorosis.^[17] 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.^[18] It is also used as a lawn conditioner,^[18] and moss killer.

In the second half of the 1850s ferrous sulfate was used as a photographic developer for collodion process images.

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.

It is used as a traditional method of treating wood panelling 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.^[19]

See also

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

References

External links

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