Sodium alum
| Names | |
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| IUPAC name
Aluminium sodium bis(sulfate) — water (1:12)
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| Other names | |
| Identifiers | |
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3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.030.239 |
| EC Number |
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| E number | E521 (acidity regulators, ...) |
PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties[1] | |
| NaAl(SO4)2·12H2O | |
| Molar mass | 458.28 g/mol |
| Appearance | white crystalline powder |
| Density | 1.6754 (20 °C) |
| Melting point | 61 °C (142 °F; 334 K) |
| 208 g/100 ml (15 °C) | |
Refractive index (nD)
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1.4388 |
| Structure[2] | |
| Cubic, cP96 | |
| Pa3, No. 205 | |
a = 1221.4 pm
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| Octahedral (Na+) Octahedral (Al3+) | |
| Hazards | |
| Flash point | non-flammable |
| Related compounds | |
Other cations
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Ammonium aluminium sulfate Potassium aluminium sulfate |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Sodium aluminium sulfate is the inorganic compound with the chemical formula NaAl(SO4)2·12H2O (sometimes written Na2SO4·Al2(SO4)3·24H2O). Also known as soda alum or sodium alum, this white solid is used in the acidity regulator of food (E521) mainly in the manufacture of baking powder.
Properties
Like its potassium analog, sodium aluminum sulfate crystallizes as the dodecahydrate in the classical cubic alum structure.
Sodium alum is very soluble in water, and is extremely difficult to purify. In the preparation of this salt, it is preferable to mix the component solutions in the cold, and to evaporate them at a temperature not exceeding 60 °C. 100 parts of water dissolve 110 parts of sodium alum at 0 °C, and 51 parts at 16 °C.[3]
Production and natural occurrence
Sodium aluminum sulfate is produced by combining sodium sulfate and aluminium sulfate. An estimated 3000 ton/y are (2003) are produced worldwide.
The dodecahydrate is known in mineralogy as alum-(Na).[4][5] Two other rare mineral forms are known: mendozite (undecahydrate)[6] and tamarugite (hexahydrate).[7]
Uses
In the US, sodium aluminum sulfate is combined with sodium bicarbonate and monocalcium phosphate in typical formulations of double acting baking powder.[8]. Sodium alum acts as an acid which is activated at baking temperatures. The aluminum content of these baking powders is seen by some consumers as a health concern.[9]
Sodium alum is also used as a food acidulant.[citation needed]
Sodium alum is also a common mordant for the preparation of hematoxylin solutions for staining cell nuclei in histopathology.
References
- ^ Weast, Robert C., ed. (1981). CRC Handbook of Chemistry and Physics (62nd ed.). Boca Raton, FL: CRC Press. p. B-146. ISBN 0-8493-0462-8..
- ^ Cromer, D. T.; Kay, M. I.; Larson, A. C. (1967), "Refinement of the alum structures. II. X-ray and neutron diffraction of NaAl(SO4)2·12H2O, γ-alum", Acta Crystallogr., 22 (2): 182–87, doi:10.1107/S0365110X67000313.
- ^ Chisholm 1911, p. 767.
- ^ Burke, Ernst A.J. (2008), "Tidying up mineral names: an IMA-CNMNC scheme for suffixes, hyphens and diacritical marks" (PDF), Mineralogical Record, 39 (2): 131–35.
- ^ Alum-(Na), WebMineral.com, retrieved 2009-11-28.Alum-(Na), Mindat.org, retrieved 2009-11-28.
- ^ Mendozite, WebMineral.com, retrieved 2009-11-28.Mendozite, Mindat.org, retrieved 2009-11-28.
- ^ Tamarugite, WebMineral.com, retrieved 2009-11-28.Tamarugite, Mindat.org, retrieved 2009-11-28.
- ^ Otto Helmboldt, L. Keith Hudson, Chanakya Misra, Karl Wefers, Wolfgang Heck, Hans Stark, Max Danner, Norbert Rösch "Aluminum Compounds, Inorganic" in Ullmann's Encyclopedia of Industrial Chemistry 2007, Wiley-VCH, Weinheim.doi:10.1002/14356007.a01_527.pub2
- ^ http://www.ewg.org/research/ewg-s-dirty-dozen-guide-food-additives/food-additive-watch-list
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