Potassium aluminium sulfate

Potassium aluminium sulfate
IUPAC name	Aluminium potassium sulfate
Other names	Potassium alum Potash alum Alum
Identifiers
CAS number	[10043-67-1], 7784-24-9 (dodecahydrate)
ChemSpider	23239
Properties
Chemical formula	KAl(SO4)2
Molar mass	258.21 g/mol
Density	1.76 g/cm3
Melting point	92–93 °C
Boiling point	200 °C
Solubility in water	36.80 g/100 g (50 °C)
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

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. 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).

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)
• Potassium Alum: Mineral Data
• Mindat