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Potassium alum

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Potassium aluminium sulfate
Aluminium potassium sulfate
Names
IUPAC name
Aluminium potassium sulfate dodecahydrate [1]
Other names
Potassium alum
Potash alum
Tawas
Identifiers
3D model (JSmol)
ECHA InfoCard 100.112.464 Edit this at Wikidata
E number E522 (acidity regulators, ...)
  • InChI=1S/Al.K.2H2O4S/c;;2*1-5(2,3)4/h;;2*(H2,1,2,3,4)/q+3;+1;;/p-4
  • [O-]S(=O)(=O)[O-].[O-]S(=O)(=O)[O-].[Al+3].[K+]
Properties
KAl(SO4)2
Molar mass 258.205 g/mol
Odor odorless
Density 1.725 g/cm3
Melting point 92–93 °C
Boiling point 200 °C
14.00 g/100 mL (20 °C)
36.80 g/100 mL (50 °C)
Solubility insoluble in acetone
1.4564
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Potassium alum, potash alum or tawas is the potassium double sulfate of aluminium. Its chemical formula is KAl(SO4)2 and it is commonly found in its dodecahydrate form as KAl(SO4)2·12(H2O). Alum is the common name for this chemical compound, given the nomenclature of potassium aluminum sulfate dodecahydrate. It is commonly used in water purification, leather tanning, fireproof textiles, and baking powder [citation needed]. It also has cosmetic uses as a deodorant, as an aftershave treatment and as a styptic for minor bleeding from shaving.

Characteristics

Potassium alum crystallizes in regular octahedra with flattened corners, and is very soluble in water. The solution reddens litmus and is an astringent. When heated to nearly a red heat it gives a porous, friable mass which is known as "burnt alum." It fuses at 92 °C in its own water of crystallization. "Neutral alum" is obtained by the addition of as much sodium carbonate to a solution of alum as will begin to cause the separation of alumina. Alum finds application as a mordant, in the preparation of lakes for sizing hand-made paper and in the clarifying of turbid liquids.

Mineral form and occurrence

Potassium alum is a naturally occurring sulfate mineral which typically occurs as encrustations on rocks in areas of weathering and oxidation of sulfide minerals and potassium-bearing minerals. In the past, alum was obtained from alunite, a mineral mined from sulfur-containing volcanic sediments source.[2] Alunite is an associate and likely potassium and aluminium source.[3][4] It has been reported at Vesuvius, Italy, east of Springsure, Queensland, Alum Cave, Tennessee, and Alum Gulch, Arizona in the United States and the island of Cebu (Philippines) locally known as tawas. A related mineral is kalunite (rock form) and kalinite, a fibrous mineral with formula KAl(SO4)2·11(H2O).[5]

Uses

Potassium alum is an astringent/styptic and antiseptic. For this reason, it can be used as a natural deodorant by inhibiting the growth of the bacteria responsible for body odor. Use of mineral salts in such a fashion does not prevent perspiration. Its astringent/styptic properties are often employed after shaving and to reduce bleeding in minor cuts and abrasions, nosebleeds, and hemorrhoids. It is frequently used topically and internally in traditional systems of medicine including Ayurveda, where it is called phitkari or saurashtri, and Traditional Chinese Medicine, where it is called ming fan.[6] It is also used as a hardener for photographic emulsions (films and papers), usually as part of the fixer, although modern materials are adequately hardened and this practice has fallen out of favor. it is also used in tanning of leather.

Toxicology and safety

Deodorant crystals containing synthetically made potassium alum are a weak irritant to the skin.[7]

See also

References

  1. ^ http://www.chemexper.com/search/cas/7784249.html
  2. ^ Bottomley (2010) p. 35
  3. ^ http://webmineral.com/data/Potassium-alum.shtml Potassium Alum: Mineral Data
  4. ^ http://www.mindat.org/show.php?id=3267 Mindat
  5. ^ http://webmineral.com/data/Kalinite.shtml Webmineral
  6. ^ http://tcm.health-info.org/Herbology.Materia.Medica/mingfan-properties.htm Uses of Alum in Traditional Chinese Medicine
  7. ^ Gallego H, Lewis EJ, Crutchfield CE 3rd (1999). "Crystal deodorant dermatitis: irritant dermatitis to alum-containing deodorant". Cutis. 64 (1): 65–6. PMID 10431678. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)

Further reading

  • Bottomley, L.; Bottomley, L.A. (2010). School of Chemistry & Bichemistry, Georgia Institute of Technology, Chemistry 1310: Laboratory Manual. Plymouth, MI: Hayden-McNeil Publishing. ISBN 978-0-7380-3819-3.{{cite book}}: CS1 maint: multiple names: authors list (link)

External links

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