Ammonium aluminium sulfate
|Ammonium aluminium sulfate|
|CAS number||, (dodecahydrate)|
|Jmol-3D images||Image 1|
|Molar mass||237.15 g/mol (anhydrous)
453.33 g/mol (dodecahydrate)
|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)|
|Crystal structure||Hexagonal (anhydrous)
|GHS signal word||WARNING|
|P264, P280, P302+352, P305+351+338, P321, P332+313, P337+313, P362|
|EU Index||not listed|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
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.
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.
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 4 to 5.
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