Iron(II) sulfate (
British English
British English (BrE, en-GB, or BE) is, according to Oxford Dictionaries, "English as used in Great Britain, as distinct from that used elsewhere". More narrowly, it can refer specifically to the English language in England, or, more broadl ...
: iron(II) sulphate) or ferrous sulfate denotes a range of
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
s 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 sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
), 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 o ...
and is
paramagnetic
Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...
. 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
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ).
Examples of substances that are commonly reducing agents include the Earth met ...
, and as such is useful for the reduction of
chromate in
cement
A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixe ...
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
Iron gall ink (also known as common ink, standard ink, oak gall ink or iron gall nut ink) is a purple-black or brown-black ink made from iron salts and tannic acids from vegetable sources. It was the standard ink formulation used in Europe for ...
. 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 fo ...
('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
Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...
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
A lawn is an area of soil-covered land planted with grasses and other durable plants such as clover which are maintained at a short height with a lawnmower (or sometimes grazing animals) and used for aesthetic and recreational purposes. ...
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
''Acer'' () is a genus of trees and shrubs commonly known as maples. The genus is placed in the family Sapindaceae.Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 nd more or less continuously updated since h ...
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
Iron gall ink (also known as common ink, standard ink, oak gall ink or iron gall nut ink) is a purple-black or brown-black ink made from iron salts and tannic acids from vegetable sources. It was the standard ink formulation used in Europe for ...
, which was used from the middle ages
In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
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 at ...
() 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
Wool is the textile fibre obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties similar to animal 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 and ...
ing as a mordant
A mordant or dye fixative is a substance used to set (i.e. bind) dyes on fabrics by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains in ...
. 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'' pl ...
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 Hydration may refer to:
* Hydrate, a substance that contains water
* Hydration enthalpy, energy released through hydrating a substance
* Hydration reaction, a chemical addition reaction where a hydroxyl group and proton are added to a compound
* ...
, and several of these forms exist in nature or were created synthetically.
* FeSO4·H2O (mineral: szomolnokite, relatively rare, monoclinic
In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic ...
)
* 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
Siderotil is an iron(II) sulfate hydrate mineral with formula: FeSO4·5H2O which forms by the dehydration of melanterite. Copper commonly occurs substituting for iron in the structure. It typically occurs as fibrous or powdery encrustations, but m ...
, relatively rare, triclinic)
* FeSO4·6H2O (mineral: ferrohexahydrite, very rare, monoclinic)
* FeSO4·7H2O (mineral: melanterite
Melanterite is a mineral form of hydrous iron(II) sulfate: FeSO4·7H2O. It is the iron analogue of the copper sulfate chalcanthite. It alters to siderotil by loss of water. It is a secondary sulfate mineral which forms from the oxidation of prim ...
, 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
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic Luster (mineralogy), lust ...
, 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-resistan ...
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
Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolu ...
from ilmenite
Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...
via the sulfate process.
Ferrous sulfate is also prepared commercially by oxidation of pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic Luster (mineralogy), lust ...
:
:2 FeS2 + 7 O2 + 2 H2O → 2 FeSO4 + 2 H2SO4
It can be produced by displacement of metals less reactive than Iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
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
Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...
ion.
On heating, iron(II) sulfate first loses its water of crystallization
In chemistry, water(s) of crystallization or water(s) of hydration are water molecules that are present inside crystals. Water is often incorporated in the formation of crystals from aqueous solutions. In some contexts, water of crystallization i ...
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 achi ...
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 a ...
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 a ...
. Thermolysis
Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is re ...
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
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...
to nitrogen monoxide and chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
to chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...
:
: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
Copper(II) sulfate, also known as copper sulphate, is an inorganic compound with the chemical formula . It forms hydrates , where ''n'' can range from 1 to 7. The pentahydrate (''n'' = 5), a bright blue crystal, is the most commonly encountered h ...
* Ammonium iron(II) sulfate, also known as ''Mohr's salt'', the common double salt of ammonium sulfate with iron(II) sulfate.
* Chalcanthum
* Ephraim Seehl known as an early manufacturer of Iron(II) sulfate, which he called 'green vitriol'.
References
External links
*
*
*
{{Authority control
Iron(II) compounds
Sulfates
World Health Organization essential medicines