Ammonium alum

Ammonium aluminium sulfate

Names
IUPAC name Aluminium ammonium bis(sulfate)
Other names Ammonium alum Tschermigite
Identifiers
CAS Number	7784-25-0 Y 7784-26-1 (dodecahydrate) Y
3D model (Jmol)	Interactive image
ChemSpider	2297489 Y 56419 (dodecahydrate) Y
ECHA InfoCard	100.029.141
EC Number	232-055-3
E number	E523 (acidity regulators, ...)
RTECS number	WS5640010
InChI InChI=1S/Al.H3N.2H2O4S/c;;2*1-5(2,3)4/h;1H3;2*(H2,1,2,3,4)/q+3;;;/p-3 Y Key: LCQXXBOSCBRNNT-UHFFFAOYSA-K Y InChI=1/Al.H3N.2H2O4S/c;;2*1-5(2,3)4/h;1H3;2*(H2,1,2,3,4)/q+3;;;/p-3 Key: LCQXXBOSCBRNNT-DFZHHIFOAY
SMILES [Al+3].[O-]S(=O)(=O)[O-].[O-]S([O-])(=O)=O.[NH4+]
Properties
Chemical formula	(NH4)Al(SO4)2
Molar mass	237.15 g/mol (anhydrous) 453.33 g/mol (dodecahydrate)
Appearance	white crystals
Density	2.45 g/cm3 (anhydrous) 1.64 g/cm3 (dodecahydrate)
Melting point	93.5 °C (200.3 °F; 366.6 K) (dodecahydrate)
Boiling point	120 °C (248 °F; 393 K) dehydr. (dodecahydrate)
Solubility in water	15 g/100 ml (20 °C, dodecahydrate)
Structure
Crystal structure	Hexagonal (anhydrous) Cubic (dodecahydrate)
Coordination geometry	Octahedral (Al3+)
Hazards
Safety data sheet	External MSDS
GHS pictograms
GHS signal word	WARNING
GHS hazard statements	H315, H319
GHS precautionary statements	P264, P280, P302+352, P305+351+338, P321, P332+313, P337+313, P362
Flash point	Non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Ammonium aluminium sulfate, also known as ammonium alum or just alum, is a white crystalline double sulfate usually encountered as the dodecahydrate, formula (NH₄)Al(SO₄)₂·12H₂O. It is used in small amounts in a variety of niche applications. The dodecahydrate occurs naturally as the rare mineral tschermigite.

Ammonium alum is made from aluminium hydroxide, sulfuric acid and ammonium sulfate. It forms a solid solution with potassium alum. Pyrolysis leaves alumina. Such alumina is used in the production of grinding powders and as precursors to synthetic gems.

Ammonium alum is not a major industrial chemical or a particularly useful laboratory reagent, but it is inexpensive and nontoxic, which invites many niche applications. It is used in water purification, in vegetable glues, in porcelain cements, in deodorants and in tanning, dyeing and in fireproofing textiles. The pH of the solution resulting from the topical application of ammonium alum with perspiration is typically in the slightly acid range, from 3 to 5.

Ammonium alum is a common ingredient in animal repellant sprays.

Aluminium sulfate, closely related to ammonium alum, is nontoxic with an LD₅₀ of 6207 mg/kg. No human or ecological (for reduced concentrations) toxicity registered.