Sodium aluminium sulfate
Aluminium sodium bis(sulfate) — water (1:12)
3D model (Jmol)
|E number||E521 (acidity regulators, ...)|
|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)
|Pa3, No. 205|
a = 1221.4 pm
|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).
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.
Production and use
It is produced by combining sodium sulfate and aluminium sulfate (SAS). An estimated 3000 ton/y are (2003) are produced. In the US, it is combined with sodium bicarbonate and monocalcium phosphate to give double acting baking powder used in domestic settings.
The classical cubic alum structure is the dodecahydrate, which is known in mineralogy as alum-(Na). Two other rare mineral forms are known: mendozite (undecahydrate) and tamarugite (hexahydrate).
In baking breads, cakes and cookies, sodium aluminum sulfate (SAS) is used as an ingredient in baking powder as a second acting agent. SAS is activated at baking temperatures and reacts with baking powder's sodium bicarbonate (baking soda) to create carbon dioxide gas bubbles that helps leaven the baked items. The uses of SAS is seen by some consumers as a health concern.
- 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.
- 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
- 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.
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