| Potassium aluminium sulfate | |
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Aluminium potassium sulfate |
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Other names
Potassium alum |
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| Identifiers | |
| CAS number | 10043-67-1 , 7784-24-9 (dodecahydrate) |
| Properties | |
| Molecular 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 | 14.00 g/100 ml (20 °C) 36.80 g/100 ml (50 °C) |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
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 . It also has cosmetic uses as a deodorant and as an aftershave treatment.
Contents |
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.
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.[1] Alunite is an associate and likely potassium and aluminium source.[2][3] 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).[4]
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.[5] 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.
Deodorant crystals containing synthetically made potassium alum are a weak irritant to the skin.[6]