Potassium alum

Potassium alum

Chembox new
Name = Potassium aluminium sulfate
ImageSize = 200px
OtherNames = potassium alum, potash alum
Section1 = Chembox Identifiers
CASNo = 7784-24-9

Section2 = Chembox Properties
Formula = KAl(SO4)2
MolarMass = 258.207 g/mol
Density = 1.76 g/cm3
Solvent = other solvents
SolubleOther = 36.80 grams of alum/100 grams of water at 50 °C
MeltingPt = 92-93 °C
BoilingPt = 200 °C

Potassium alum or potash alum 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). It is commonly used in water purification, leather tanning, fireproof textiles, and baking powder. It also has cosmetic uses as a deodorant and as an aftershave treatment.


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. Alunite is an associate and likely potassium and aluminium source. [http://webmineral.com/data/Potassium-alum.shtml Potassium Alum: Mineral Data] [http://www.mindat.org/show.php?id=3267 Mindat] 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 "kalinite", a fibrous mineral with formula KAl(SO4)2·11(H2O). [http://webmineral.com/data/Kalinite.shtml Webmineral]


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. [http://tcm.health-info.org/Herbology.Materia.Medica/mingfan-properties.htm Uses of Alum in Traditional Chinese Medicine]


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Look at other dictionaries:

  • potassium alum — n ALUM (1a) * * * [USP] alum prepared with the addition of potassium; used topically as an astringent …   Medical dictionary

  • potassium alum — noun a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum • Syn: ↑alum, ↑potash alum • Hypernyms: ↑aluminum, ↑aluminium, ↑Al, ↑atomic number 13, ↑double salt * * * …   Useful english dictionary

  • potassium alum — Chem. alum1 (def. 1). * * * …   Universalium

  • aluminium-potassium alum — aliuminio kalio alūnas statusas T sritis chemija formulė KAl(SO₄)₂·12H₂O atitikmenys: angl. aluminium potassium alum; aluminium potassium sulfate rus. алюминиево калиевые квасцы ryšiai: sinonimas – aliuminio kalio bis(tetraoksosulfatas)… …   Chemijos terminų aiškinamasis žodynas

  • Alum — This article is about the chemical compound. For other uses, see Alum (disambiguation). Bulk alum Alum (  / …   Wikipedia

  • alum — alum1 /al euhm/, n. Chem. 1. Also called potash alum, potassium alum. a crystalline solid, aluminum potassium sulfate, K2SO4·Al2(SO4)3·24H2O, used in medicine as an astringent and styptic, in dyeing and tanning, and in many technical processes. 2 …   Universalium

  • alum — A double sulfate of aluminum and of an alkaline earth element or ammonium; chemically, an a. is any one of the markedly astringent double salts formed by a combination of a sulfate of aluminum, iron, manga …   Medical dictionary

  • alum — /ˈæləm / (say aluhm) noun 1. an astringent crystalline substance, a double sulphate of aluminium and potassium, K2SO4.Al2(SO4)3.24H2O, or KAl(SO4)2.12H2O, used in medicine, dyeing, and many technical processes. 2. one of a class of double… …   Australian-English dictionary

  • alum — alum1 [al′əm] n. [ME & OFr < L alumen, alum: for IE base see ALE] 1. a double sulfate of a monovalent metal or radical (as sodium, potassium, or ammonium) with a trivalent metal (as aluminum, iron, or chromium): it is used as an astringent, as …   English World dictionary

  • Alum — Al um, n. [OE. alum, alom, OF. alum, F. alun, fr. L. alumen alum.] (Chem.) A double sulphate formed of aluminium and some other element (esp. an alkali metal) or of aluminium. It has twenty four molecules of water of crystallization. [1913… …   The Collaborative International Dictionary of English

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