Iron(II) sulfate

Iron(II) sulfate

iron(II) sulfate, when dissolved in water
Names
IUPAC name Iron(II) sulfate
Other names Ferrous sulfate, Green vitriol, Iron vitriol, Copperas, Melanterite, Szomolnokite
Identifiers
CAS Number	anhydrous: 7720-78-7 Y monohydrate: 17375-41-6 N heptahydrate: 7782-63-0 N
3D model (JSmol)	anhydrous: Interactive image
ChEBI	anhydrous: CHEBI:75832 N
ChemSpider	anhydrous: 22804 Y monohydrate: 56459 N heptahydrate: 22804 N
ECHA InfoCard	100.028.867
EC Number	231-753-5
PubChem CID	anhydrous: 24393 monohydrate: 62712 heptahydrate: 62662
RTECS number	NO8500000 (anhydrous) NO8510000 (heptahydrate)
UNII	anhydrous: 2IDP3X9OUD N monohydrate: RIB00980VW N dihydrate: G0Z5449449 N heptahydrate: 39R4TAN1VT N
UN number	3077
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 anhydrous: InChI=1/Fe.H2O4S/c;1-5(2,3)4/h;(H2,1,2,3,4)/q+2;/p-2 Key: BAUYGSIQEAFULO-NUQVWONBAS
SMILES anhydrous: [O-]S(=O)(=O)[O-].[Fe+2]
Properties
Chemical formula	FeSO4
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)
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)	6998124000000000000♠1.24×10−2 cm3/mol (anhydrous) 6998105000000000000♠1.05×10−2 cm3/mol (monohydrate) 6998112000000000000♠1.12×10−2 cm3/mol (heptahydrate)[3] 6998101999999999999♠+10200×10−6 cm3/mol
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] 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]
Pharmacology
ATC code	B03AA07 (WHO)
Hazards
GHS pictograms	[7]
GHS signal word	Warning
GHS hazard statements	H302, H315, H319[7]
GHS precautionary statements	P305+351+338[7]
NFPA 704	[5] 1 2 1
Lethal dose or concentration (LD, LC):
LD50 (median 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 otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

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, the blue-green heptahydrate 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.^[14]

It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system.^[15]

Uses

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.^[16]

Medical use

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.

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 (c.588–586 BCE) showed the possible presence of iron.^[17] It is thought that oak galls and copperas may have been used in making the ink on those letters.^[18] 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.^[19]

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

Other uses

In horticulture it is used for treating iron chlorosis.^[20] 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.^[21] It is also used as a lawn conditioner,^[21] 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.^[22]

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)

Anhydrous iron(II) sulfate

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.^[6]

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 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.^[23]

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

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 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 monoxide 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

Iron(II) sulfate outside a titanium dioxide factory in Kaanaa, Pori, Finland.

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

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

See also

• Iron(III) sulfate (ferric sulfate), the other common simple sulfate of iron.
• Copper(II) sulfate
• Ammonium iron(II) sulfate, also known as Mohr's salt, the common double salt of ammonium sulfate with iron(II) sulfate.
• Ephraim Seehl known as an early manufacturer of green vitriol.^[24]

References

External links

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