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 , where is a valence (chemistry), monovalent cation such as potassium or a ...

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' colour, 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, d ...

acidic In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...

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,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

s. It is a weak oxidizing agent, capable of being reduced to

Mohr's salt Ammonium iron(II) sulfate, or Mohr's salt, is the inorganic compound with the formula (NH4)2Fe(SO4)2(H2O)6. Containing two different cations, Fe2+ and NH4+, it is classified as a double salt of ferrous sulfate and ammonium sulfate. It is a commo ...

, ferrous ammonium sulfate.

Preparation

FAS can be prepared by crystallization from a solution of

ferric sulfate Iron(III) sulfate (or ferric sulfate), is a family of inorganic compounds with the formula Fe2(SO4)3(H2O)n. A variety of hydrates are known, including the most commonly encountered form of "ferric sulfate". Solutions are used in dyeing as a morda ...

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 and

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 nitri ...

. 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: 6 FeSO₄ + 2 HNO₃ + 3 H₂SO₄ = 3 Fe₂(SO₄)₃ + 2 NO + 4 H₂O Synthesis: Fe₂(SO₄)₃ + (NH₄)₂SO₄ = 2 NH₄Fe(SO₄)₂

Uses

Areas of use for FAS include

waste water Wastewater 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 domestic, industrial ...

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

tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...

, production of dyestuffs, 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 types ...

agent in the production of

electronic components An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not ...

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

refrigeration The term refrigeration refers to the process of removing heat from an enclosed space or substance for the purpose of lowering the temperature.International Dictionary of Refrigeration, http://dictionary.iifiir.org/search.phpASHRAE Terminology, ht ...

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 special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

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