*** Welcome to piglix ***

Ferric ammonium sulfate

Ammonium iron(III) sulfate
Ferric amm sulfate.jpg
Ferric Ammonium Sulfate Dodecahydrate formula.png
Names
IUPAC name
Ammonium iron(III) sulfate
Other names
Ferric ammonium sulfate
Ferric alum
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.107.412
EC Number 233-382-4
PubChem CID
UNII
Properties
FeNH4(SO4)2•12H2O
Molar mass 482.25 g/mol (dodecahydrate)
Appearance Pale violet octahedral crystals
Odor weak ammonia-like
Density 1.71 g/cm3
Melting point 39 to 41 °C (102 to 106 °F; 312 to 314 K)
1240 g/L
Hazards
Main hazards Irritant (Xi)
Related compounds
Other anions
Ammonium iron(III) citrate
Ammonium chloride
Other cations
Ammonium aluminium sulfate
potassium aluminium sulfate
Related compounds
Ammonium iron(II) sulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Ammonium iron(III) sulfate, NH4Fe(SO4)2·12 H2O, or NH4[Fe(H2O)6](SO4)2·6 H2O, also known as ferric ammonium sulfate (FAS) or iron alum, is a double salt in the class of alums, which consists of compounds with the general formula AB(SO4)2 · 12 H2O. It has the appearance of weakly violet, octahedrical crystals. 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,acidic and toxic towards microorganisms. It is a weak oxidizing agent, capable of being reduced to Mohr's salt, ferrous ammonium sulfate.

FAS can be prepared by crystallization from a solution of ferric sulfate and ammonium sulfate. Iron(II) in ferrous sulfate is oxidized to Iron(III) in ferric sulfate by addition of sulfuric and nitric acid. Upon addition of ammonium sulfate to the solution and damping in of the solution, ferric ammonium sulfate crystals will precipitate.

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

Procedure:

The nitric and sulfuric acid is reacted with the ferrous sulfate to make ferric sulfate, nitric oxide, and water. The ferric sulfate is mixed with ammonium sulfate and crystallized to get ammonium iron(III) sulfate. The solution is normally tested to ensure that no more iron(II) is left.

Crystals of ferric ammonium sulfate


...
Wikipedia

...