Ammonium alum

Ammonium aluminium sulfate, also known as ammonium alum or just alum (though there are many different substances also called "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.^[1]

Ammonium alum

Names
Other names Ammonium alum sulfate Tschermigite
Identifiers
CAS Number	7784-25-0 Y 7784-26-1 (dodecahydrate) Y
3D model (JSmol)	Interactive image
ChemSpider	2297489 Y 56419 (dodecahydrate) Y
ECHA InfoCard	100.029.141
EC Number	232-055-3 616-522-2 (dodecahydrate)
E number	E523 (acidity regulators, ...)
KEGG	D02842 (dodecahydrate)
PubChem CID	3032540 62668 (dodecahydrate)
RTECS number	WS5640010
UNII	DPU64XYB1D Y 5C36DRL9ZN (dodecahydrate) Y
CompTox Dashboard (EPA)	DTXSID7051428
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[1]
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[1]
Crystal structure	Hexagonal (anhydrous) Cubic (dodecahydrate)
Coordination geometry	Octahedral (Al3+)
Hazards[2]
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H315, H319
Precautionary statements	P264, P280, P302+P352, P305+P351+P338, P321, P332+P313, P337+P313, P362
Flash point	Non-flammable
Safety data sheet (SDS)	External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Production and basic properties

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.^[3]

Uses

Ammonium alum is not a major industrial chemical or a particularly useful laboratory reagent, but it is cheap and effective, 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.^[4] 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.^[5]

Ammonium alum is a common ingredient in animal repellent sprays.^[6][7][8]