Ammonium iron(III) sulfate, NH₄Fe(SO₄)₂·12 H₂O, or NH₄ e(H₂O)₆SO₄)₂·6 H₂O, also known as ferric ammonium sulfate (FAS) or iron alum, is a

double salt A double salt is a salt that contains two or more different cations or anions. Examples of double salts include alums (with the general formula ) and Tutton's salts (with the general formula ). Other examples include potassium sodium tartrate, a ...

in the class of

alum An alum () is a type of chemical compound, usually a hydrated double salt, double sulfate salt (chemistry), salt of aluminium with the general chemical formula, formula , such that is a valence (chemistry), monovalent cation such as potassium ...

s, which consists of compounds with the general formula AB(SO₄)₂ · 12 H₂O. It has the appearance of weakly violet, octahedrical

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

s. There has been some discussion regarding the origin of the crystals' color, with some ascribing it to impurities in the compound, and others claiming it to be a property of the crystal itself. FAS 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, ...

acidic An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen cation, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the ...

and

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...

towards

microorganism A microorganism, or microbe, is an organism of microscopic scale, microscopic size, which may exist in its unicellular organism, single-celled form or as a Colony (biology)#Microbial colonies, colony of cells. The possible existence of unseen ...

s. It is a weak oxidizing agent, capable of being reduced to Mohr's salt, ferrous ammonium sulfate.

Preparation

FAS can be prepared by crystallization from a solution of

ferric sulfate Iron(III) sulfate or ferric sulfate (British English: sulphate instead of sulfate) is a family of inorganic compounds with the formula Fe2(SO4)3(H2O)n. A variety of water of crystallization, hydrates are known, including the most commonly encount ...

and

ammonium sulfate Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English); (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen a ...

. Iron(II) in ferrous sulfate is oxidized to ferric sulfate by addition of

sulfuric Sulfur (American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form ...

and

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 ...

. Upon addition of ammonium sulfate to the solution and damping in of the solution, ferric ammonium sulfate crystals precipitate. Equations for these conversions ignore the degree of hydration of the material. :Oxidation: :Synthesis:

Uses

Areas of use for FAS include

waste water Wastewater (or waste water) is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of do ...

treatment,''Wiley Encyclopedia of inorganic chemistry'': Volume 4, p. 1704: tanning, production of

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 ...

stuffs, and as an

etching Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other type ...

agent in the production of

electronic components An electronic component is any basic discrete electronic device or physical entity part of an Electronics, electronic system used to affect electrons or their associated electromagnetic field, fields. Electronic components are mostly industrial ...

. It has been used in a wide area of applications, including adiabatic

refrigeration Refrigeration is any of various types of cooling of a space, substance, or system to lower and/or maintain its temperature below the ambient one (while the removed heat is ejected to a place of higher temperature).IIR International Dictionary of ...

equipment, biochemical

analysis Analysis (: analyses) is the process of breaking a complex topic or substance into smaller parts in order to gain a better understanding of it. The technique has been applied in the study of mathematics and logic since before Aristotle (38 ...

, and

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

Gallery

Ammoniumeisenalaun.jpg, Crystals of ferric ammonium sulfate Ammonium iron(III) sulfate dodecahydrate in moist air, 2015-10-22 (1).jpg, Crystals of ammonium iron(III) sulfate after 16 days in the air

References

{{DEFAULTSORT:Ammonium Iron(Iii) Sulfate Ammonium compounds Iron(III) compounds Sulfates Double salts