ferrous sulfate

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
EC number	231-753-5
RTECS number	NO8500000
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
Density	2.84 g/cm3 (anhydrous) 1.898 g/cm3 (heptahydrate)
Melting point	400 °C (decomp)
Solubility in water	25.6 g/100mL (anhydrous)
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
Related compounds
Related compounds	Iron(III) sulfate
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Iron(II) sulfate (Iron(II) sulphate) or ferrous sulfate (ferrous sulphate) is the chemical compound with the formula (FeSO₄), known since ancient times as copperas. It is most commonly encountered as the blue-green heptahydrate.

Hydrates

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, relatively common)

At 90°C, the heptahydrate, also called green vitriol or copperas, 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 dehydratation 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.^[1]

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 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 reducing agent. For example, it reduces nitric acid to nitrogen oxide and chlorine to chloride:

6 Fe²⁺ + 6 H⁺ + 2 HNO₃ → 6 Fe³⁺ + 4 H₂O + 2 NO

2 Fe²⁺ + Cl₂ → 2 Fe³⁺ + 2 Cl^-

Ferrous sulfate outside titanium dioxide factory in Kaanaa, Pori.

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. It also finds use in wool dyeing as a mordant.

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.

Ferrous sulfate can also be used to stain concrete and some limestones and sandstones a yellowish rust color.^[2]

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

Other uses

In horticulture it is used for treating iron chlorosis.^[3] 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.^[4] It is also used as a lawn conditioner,^[4] 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 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.

See also

• 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

1. ^ Egon Wildermuth, Hans Stark, Gabriele Friedrich, Franz Ludwig Ebenhöch, Brigitte Kühborth, Jack Silver, Rafael Rituper “Iron Compounds” in Ullmann’s Encyclopedia of Industrial Chemistry Wiley-VCH, Wienheim, 2005.
2. ^ How To Stain Concrete with Iron Sulfate
3. ^ Koenig, Rich and Kuhns, Mike: Control of Iron Chlorosis in Ornamental and Crop Plants. (Utah State University, Salt Lake City, August 1996) p.3
4. ^ ^{a b} Handreck, Kevin (2002). Gardening Down Under: A Guide to Healthier Soils and Plants (2nd ed.). Collingwood, Victoria: CSIRO Publishing. pp. 146-47. ISBN 0-643-06677-2. 

External links