Potassium aluminium sulfate

"Potassium alum" redirects here. For the mineral form, see Alum-(K).

Potassium aluminium sulfate dodecahydrate IUPAC name Aluminium potassium bis(sulfate) — water (1:12) Other names Potassium alum Potash alum Alum Kalinite Identifiers InChI InChI=1/Al.K.2H2O4S.12H2O/c;;2* 1-5(2,3)4;;;;;;;;;;;;/h;;2*(H2 ,1,2,3,4);12*1H2/q+3;+1;;;;;;; ;;;;;;;/p-4 InChIKey GNHOJBNSNUXZQA-XBHQNQODAI Standard InChI InChI=1S/Al.K.2H2O4S.12H2O/c;;2 *1-5(2,3)4;;;;;;;;;;;;/h;;2*(H 2,1,2,3,4);12*1H2/q+3;+1;;;;;; ;;;;;;;;/p-4 Standard InChIKey GNHOJBNSNUXZQA-UHFFFAOYSA-J CAS number [7784-24-9] EC number 233-141-3 ChemSpider 56418 Properties Chemical formula KAl(SO4)2·12H2O Molar mass 474.39 g/mol Density 1.757 g/cm3 (20 °C) Melting point 64.5 °C (−9H2O) 92.5 °C Boiling point 200 °C dehydr. Solubility in water 11.4 g/100 ml (20 °C) Refractive index (nD) 1.454 Structure Crystal structure Cubic, cP96 Space group Pa3, No. 205 Lattice constant a = 1216.40(5) pm Coordination geometry Octahedral (K+) Octahedral (Al3+) Hazards EU index number not listed Flash point non-flammable Related compounds Other cations Sodium aluminium sulfate Ammonium aluminium sulfate Potassium chromium(III) sulfate  Template:Tick(what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Potassium aluminium sulfate (anhydrous) IUPAC name Aluminium potassium bis(sulfate) Identifiers InChI InChI=1/Al.K.2H2O4S/c;;2*1-5(2,3)4/h;;2*(H2,1,2,3,4)/q+3;+1;;/p-4 InChIKey GRLPQNLYRHEGIJ-XBHQNQODAE Standard InChI InChI=1S/Al.K.2H2O4S/c;;2*1-5(2,3)4/h;;2*(H2,1,2,3,4)/q+3;+1;;/p-​4 Standard InChIKey GRLPQNLYRHEGIJ-UHFFFAOYSA-J CAS number [10043-67-1] EC number 233-141-3 ChemSpider 23239 Properties Chemical formula KAl(SO4)2 Molar mass 258.21 g/mol Hazards EU index number not listed GHS pictograms GHS signal word WARNING GHS hazard statements H302, H315, H319 GHS precautionary statements P234, P264, P270, P280, P301+312, P302+352, P305+351+338, P321, P330, P332+313, P337+313, P362, P390, P406 Flash point non-flammable  Template:Tick(what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Potassium aluminium sulfate, better known as potassium alum or potash alum, is the double sulfate of aluminium and potassium. Its chemical formula is KAl(SO₄)₂ and it is commonly found in its dodecahydrate form as KAl(SO₄)₂·12(H₂O). The dodechydrate is sometimes commercialised as alum: this name is ambiguous in chemical nomenclature, as potassium aluminium sulfate is one of several alums (double sulfates of aluminium with a monovalent cation). It is commonly used in water purification, leather tanning, fireproof textiles, and baking powder. It also has uses as a deodorant, as an aftershave treatment and as acidity regulator in food (E522).

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

The mineral form of potassium alum is officially known as alum-(K). It 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. It has been reported at

• Vesuvius, Italy
• east of Springsure, Queensland
• Alum Cave, Tennessee
• Alum Gulch, Arizona
• the island of Cebu (Philippines), locally known as tawas.

Kalinite, a fibrous mineral, was once thought to be the undecahydrate, but is now believed to be chemically identical to Alum-(K).

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.

External links

• NIOSH Pocket Guide to Chemical Hazards 0024
• IPCS Environmental Health Criteria 194: Aluminium
• NLM Hazardous Substances Data Bank entry for Alum, potassium
• FAO/WHO Joint Expert Committee on Food Additives (JECFA) monograph: Aluminium (WHO Food Additives Series 24)