Iron(II) sulfate (
British English: iron(II) sulphate) or ferrous sulfate denotes a range of
salts with the formula
Fe SO4·''x''H
2O. These compounds exist most commonly as the hepta
hydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
(''x'' = 7) but several values for x are known. 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
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
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 2O)6">e(H2O)6sup>2+, which has
octahedral molecular geometry
In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The oc ...
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.
It is on the
World Health Organization's List of Essential Medicines.
In 2020, it was the 116th most commonly prescribed medication in the United States, with more than 5million prescriptions.
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
iron gall ink. The preparation of
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
('oil of vitriol') by the distillation of green vitriol (Iron(II) sulfate) has been known for at least 700 years.
Medical use
Plant growth
Iron(II) sulfate is sold as ferrous sulfate, a soil amendment for lowering the pH of a high alkaline soil so that plants can access the soil's nutrients.
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.
Ferrous sulfate can be used as a
lawn conditioner.
[ It can also be used to eliminate silvery thread moss in golf course putting greens.
]
Pigment and craft
Ferrous sulfate can be used to stain concrete and some limestones and sandstones a yellowish rust color.[How To Stain Concrete with Iron Sulfate](_blank)
/ref>
Woodworkers use ferrous sulfate solutions to color maple wood a silvery hue.
Green vitriol is also a useful reagent in the identification of mushrooms.
Historical uses
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
The Lachish Letters or ''Lachish Ostraca'', sometimes called ''Hoshaiah Letters'', are a series of letters written in carbon ink containing Canaanite inscriptions in Ancient Hebrew on clay ostraca. The letters were discovered at the excavations ...
() 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 dye
A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution an ...
ing 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
Indigo dye is an organic compound with a distinctive blue color. Historically, indigo was a natural dye extracted from the leaves of some plants of the ''Indigofera'' genus, in particular ''Indigofera tinctoria''; dye-bearing ''Indigofera'' pla ...
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.
In the second half of the 1850s ferrous sulfate was used as a photographic developer for collodion process
The collodion process is an early photographic process. The collodion process, mostly synonymous with the "collodion wet plate process", requires the photographic material to be coated, sensitized, exposed, and developed within the span of about ...
images.
Hydrates
Iron(II) sulfate can be found in various states of hydration, and several of these forms exist in nature or were created synthetically.
* FeSO4·H2O (mineral: szomolnokite
Szomolnokite (Fe2+SO4·H2O) is a monoclinic iron sulfate mineral forming a complete solid solution with magnesium end-member kieserite (MgSO4·H2O). In 1877 szomolnokite's name was derived by Joseph Krenner from its type locality of oxidized sulfi ...
, relatively rare, monoclinic)
* FeSO4·H2O (synthetic compound stable at pressures exceeding 6.2 GPa, triclinic)
* FeSO4·4H2O (mineral: rozenite, white, relatively common, may be dehydration product of melanterite, monoclinic)
* FeSO4·5H2O (mineral: siderotil, relatively rare, triclinic)
* FeSO4·6H2O (mineral: ferrohexahydrite, very rare, monoclinic)
* FeSO4·7H2O (mineral: melanterite, blue-green, relatively common, monoclinic)
The tetrahydrate is stabilized when the temperature of aqueous solutions reaches . At these solutions form both the tetrahydrate and monohydrate.
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
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
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
Reactions
Upon dissolving in water, ferrous sulfates form the metal aquo complex 2O)6">e(H2O)6sup>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
A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...
solid. When further heated, the anhydrous material decomposes into sulfur dioxide
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...
and sulfur trioxide
Sulfur trioxide (alternative spelling sulphur trioxide, also known as ''nisso sulfan'') is the chemical compound with the formula SO3. It has been described as "unquestionably the most important economically" sulfur oxide. It is prepared on an ind ...
, leaving a reddish-brown iron(III) oxide
Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally ...
. Thermolysis of iron(II) sulfate begins at about .
:2FeSO_4-> Deltae_2O_3 + SO_2 + SO_3
Like other 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
Its mild reducing power is of value in organic synthesis. It is used as the iron catalyst component of Fenton's reagent.
Ferrous sulfate can be detected by the cerimetric method, which is the official method of the Indian Pharmacopoeia. This method includes the use of ferroin solution showing a red to light green colour change during titration.
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.
*Chalcanthum
In alchemy, chalcanthum, also called chalcanth or calcanthum, was a term used for the compound blue vitriol (CuSO4), and the ink made from it. The term was also applied to red vitriol (a native sulfate of cobalt), and to green vitriol (ferrous su ...
*Ephraim Seehl
Ephraim Reinhold Seehl ( en, Ephraim Rinhold Seehl) (died after 1790) was an apothecary and chemist of German background, born in Sweden. He was known as a manufacturer of green vitriol.
Life
He was the son of Captain Reinhold Seehl (d. 1721), a ...
known as an early manufacturer of Iron(II) sulfate, which he called 'green vitriol'.
References
External links
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{{Authority control
Iron(II) compounds
Sulfates
World Health Organization essential medicines