Ammonium alum

Chemical compound From Wikipedia, the free encyclopedia

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]

Quick facts Names, Identifiers ...
Ammonium alum
Names
Other names
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.141 Edit this at Wikidata
EC Number
  • 232-055-3 616-522-2 (dodecahydrate)
E number E523 (acidity regulators, ...)
KEGG
RTECS number
  • WS5640010
UNII
  • InChI=1S/Al.H3N.2H2O4S/c;;2*1-5(2,3)4/h;1H3;2*(H2,1,2,3,4)/q+3;;;/p-3 checkY
    Key: LCQXXBOSCBRNNT-UHFFFAOYSA-K checkY
  • 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
  • [Al+3].[O-]S(=O)(=O)[O-].[O-]S([O-])(=O)=O.[NH4+]
Properties[1]
(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)
15 g/100 ml (20 °C, dodecahydrate)
Structure[1]
Hexagonal (anhydrous)
Cubic (dodecahydrate)
Octahedral (Al3+)
Hazards[2]
GHS labelling:
Skin Irrit. 2; Eye Irrit. 2
Warning
H315, H319
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).
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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]

References

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