Iron(II) sulfate or ferrous sulfate (

British English British English is the set of Variety (linguistics), varieties of the English language native to the United Kingdom, especially Great Britain. More narrowly, it can refer specifically to the English language in England, or, more broadly, to ...

: sulphate instead of sulfate) denotes a range of

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

s with the formula Fe SO₄·''x''H₂O. These compounds exist most commonly as the heptahydrate (''x'' = 7), but several values for x are known. The hydrated form is used medically to treat or prevent

iron deficiency Iron deficiency, or sideropenia, is the state in which a body lacks enough iron to supply its needs. Iron is present in all cells in the human body and has several vital functions, such as carrying oxygen to the tissues from the lungs as a key ...

, and also for industrial applications. Known since ancient times as copperas and as green vitriol (

vitriol Vitriol is the general chemical name encompassing a class of chemical compounds comprising sulfates of certain metalsoriginally, iron or copper. Those mineral substances were distinguished by their color, such as green vitriol for hydrated iron(I ...

is an archaic name for hydrated sulfate minerals), 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 In chemistry, metal aquo complexes are coordination compounds containing metal ions with only water as a ligand. These complexes are the predominant species in aqueous solutions of many metal salts, such as metal nitrates, sulfates, and perchlorat ...

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 The WHO Model List of Essential Medicines (aka Essential Medicines List or EML), published by the World Health Organization (WHO), contains the medications considered to be most effective and safe to meet the most important needs in a health s ...

. In 2022, it was the 107th most commonly prescribed medication in the United States, with more than 6million 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 common reducing agents include hydrogen, carbon ...

, 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 mi ...

to less toxic Cr(III) compounds. Historically, ferrous sulfate was used in the textile industry for centuries as a

dye fixative A mordant or dye fixative is a substance used to set (i.e., bind) dyes on fabrics. It does this 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 ...

. 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 t ...

. The preparation of

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

('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 (from ) is the art and science of growing fruits, vegetables, flowers, trees, shrubs and ornamental plants. Horticulture is commonly associated with the more professional and technical aspects of plant cultivation on a smaller and mo ...

, it is used for treating iron

chlorosis In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...

. 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 Poaceae, grasses and other durable plants such as clover lawn, clover which are maintained at a short height with a lawn mower (or sometimes grazing animals) and used for aesthetic an ...

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
/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 soapberry family Sapindaceae.Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 nd more or less continuously updated si ...

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

ink Ink is a gel, sol, or solution that contains at least one colorant, such as a dye or pigment, and is used to color a surface to produce an image, text, or design. Ink is used for drawing or writing with a pen, brush, reed pen, or quill. ...

s, most notably

, which was used from the

Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of global history. It began with the fall of the Western Roman Empire and ...

until the end of the 18th century. Chemical tests made on the

Lachish letters The Lachish Letters are a series of letters written in carbon ink containing ancient Israelite inscriptions in Ancient Hebrew on clay ostraca. The letters were discovered at the excavations at Lachish (Tell ed-Duweir). The ostraca were discov ...

() 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 fiber 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 some properties similar to animal w ...

dye Juan de Guillebon, better known by his stage name DyE, is a French musician. He is known for the music video of the single "Fantasy Fantasy is a genre of speculative fiction that involves supernatural or Magic (supernatural), magical ele ...

ing as a

mordant A mordant or dye fixative is a substance used to set (i.e., bind) dyes on fabrics. It does this 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 ...

. Harewood, a material used in

marquetry Marquetry (also spelled as marqueterie; from the French ''marqueter'', to variegate) is the art and craft of applying pieces of wood veneer, veneer to a structure to form decorative patterns or designs. The technique may be applied to case furn ...

and

parquetry Parquet (; French for "a small compartment") is a geometric mosaic of wood pieces used for decorative effect in flooring. Parquet patterns are often entirely geometrical and angular—squares, triangles, Lozenge (shape), lozenges—but may co ...

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 indigo, blue color. Indigo is a natural dye obtained from the leaves of some plants of the Indigofera#Uses, ''Indigofera'' genus, in particular ''Indigofera tinctoria''. Dye-bearing ''Indigofer ...

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 photography, photographic process for the production of grayscale images. The collodion process – mostly synonymized with the term "''wet-plate process''", requires the photographic material to be coated, sensi ...

images.

Hydrates

left, 120px, portion of the solid ferrous sulfate heptahydrate. One water of crystallization is evident. 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, relatively rare,

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...

) * FeSO₄·H₂O (synthetic compound stable at pressures exceeding 6.2 GPa,

triclinic class=skin-invert-image, 180px, Triclinic (a ≠ b ≠ c ≠ a and α, β, γ, 90° pairwise different) In crystallography, the triclinic (or anorthic) crystal system is one of the seven crystal systems. A crystal system is described by three b ...

) * 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 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 Dehydration, loss of water. It is a secondary sulfate mineral which forms from the oxida ...

, 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 Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue ...

marcasite The mineral marcasite, sometimes called "white iron pyrite", is iron sulfide (FeS2) with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both ...

chalcopyrite Chalcopyrite ( ) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a Mohs scale, hardness of 3.5 to 4 ...

, 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 of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

before 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. : 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 derived from titanium with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or Colour Index Internationa ...

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, printi ...

via the sulfate process. Ferrous sulfate is also prepared commercially by oxidation of

: : It can be produced by displacement of metals less reactive than

Iron Iron is a chemical element; it has symbol Fe () 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, forming much of Earth's o ...

from solutions of their sulfate: :

Reactions

Upon dissolving in water, ferrous sulfates form the

metal aquo complex In chemistry, metal aquo complexes are coordination compounds containing metal ions with only water as a ligand. These complexes are the predominant species in aqueous solutions of many metal salts, such as metal nitrates, sulfates, and perchlo ...

e(H₂O)₆sup>2+, which is an almost colorless,

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 is ...

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 colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...

and

sulfur trioxide Sulfur trioxide (alternative spelling sulphur trioxide) is the chemical compound with the formula SO3. It has been described as "unquestionably the most conomicallyimportant sulfur oxide". It is prepared on an industrial scale as a precursor to ...

, leaving a reddish-brown

iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound with the formula . It occurs in nature as the mineral hematite, which serves as the primary source of iron for the steel industry. It is also known as red iron oxide, especially when use ...

. Thermolysis of iron(II) sulfate begins at about . : Like other iron(II) salts, iron(II) sulfate is a reducing agent. For example, it reduces

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

to nitrogen monoxide and

chlorine Chlorine is a chemical element; it has Symbol (chemistry), 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 ...

chloride The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...

: : : Its mild reducing power is of value in organic synthesis. It is used as the iron catalyst component of

Fenton's reagent Fenton's reagent is a solution of hydrogen peroxide (H2O2) and an iron catalyst (typically iron(II) sulfate, FeSO4). It is used to oxidize contaminants or waste water as part of an advanced oxidation process. Fenton's reagent can be used to destro ...

. 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.

References

External links

* * {{Authority control Iron(II) compounds Sulfates World Health Organization essential medicines Deliquescent materials