Iron(II) sulfate

Overview
Iron(II) sulfate is the chemical compound with the formula (FeSO4). Also known as ferrous sulphate, or copperas, iron(II) sulfate is most commonly encountered as the blue-green heptahydrate. In its anhydrous, crystalline state, its standard enthalpy of formation is ΔfH°solid = -928.4 kJ.mol-1 and its standard molar entropy is S°solid = 107.5 J.K-1.mol-1.

Hydrates
Iron(II) sulfate can be found in various states of hydration, and several of these forms exist in nature. At 90°C, the heptahydrate loses water to form the colourless monohydrate, also called green vitriol or copperas.
 * FeSO4·H2O (mineral: szomolnokite)
 * FeSO4·4H2O
 * FeSO4·5H2O (mineral: siderotil)
 * FeSO4·7H2O (mineral: melanterite)

Production
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 waste product. Iron(II) sulfate is prepared commercially by oxidation of pyrite, or by treating iron with sulfuric acid.

Uses
Ferrous sulfate is 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.

Large quantities of this salt are used as a reducing agent, mostly for the reduction of chromate in cement.

Nutrition
Ferrous sulfate is used to treat iron-deficiency anemia. Side effects of therapy may include nausea and epigastric abdominal discomfort after taking iron. These side effects may be minimized by taking ferrous sulfate at bedtime. Copperas was given indiscriminately by untrained persons to slaves in the 18th and 19th centuries for various ailments. The knowledge that it would cause violent nausea and vomiting made it an ideal "remedy" for virtually anything that ailed a slave and kept him from work. Many slaves were poisoned and died from this practice.

Ferrous sulfate is also used to fortify various foods with iron, for example, the enriched corn meal in Cheetos.

Colouring
Ferrous sulfate is used in the manufacture of inks, most notably iron gall ink, which was used from the middle ages until the American Revolution. 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 a yellowish rust colour.

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

Other uses
In horticulture it is used as a lawn conditioner 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 an erosion-resistant, protective coating on the inside of the tube.