Sodium aluminium sulfate

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Sodium aluminium sulfate
CAS number 10102-71-3
7784-28-3 (dodecahydrate)
PubChem 24939
ChemSpider 22972
EC-number 233-277-3
Jmol-3D images Image 1
Molecular formula 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)
Solubility in water 208 g/100 ml (15 °C)
Refractive index (nD) 1.4388
Crystal structure Cubic, cP96
Space group Pa3, No. 205
Lattice constant a = 1221.4 pm
Octahedral (Na+)
Octahedral (Al3+)
EU Index not listed
Flash point non-flammable
Related compounds
Other cations Ammonium aluminium sulfate
Potassium aluminium sulfate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

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[edit]

It is produced by combining sodium sulfate and aluminium sulfate. 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.[2]

The classical cubic alum structure is the dodecahydrate, which is known in mineralogy as alum-(Na).[3][4] Two other rare mineral forms are known: mendozite (undecahydrate)[5] and tamarugite (hexahydrate).[6]

It is also a common mordant for the preparation of hematoxylin solutions for staining cell nuclei in histopathology.


  1. ^ 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. .
  2. ^ 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
  3. ^ Burke, Ernst A.J. (2008), "Tidying up mineral names: an IMA-CNMNC scheme for suffixes, hyphens and diacritical marks", Mineralogical Record 39 (2): 131–35 .
  4. ^ Alum-(Na),, retrieved 2009-11-28 .Alum-(Na),, retrieved 2009-11-28 .
  5. ^ Mendozite,, retrieved 2009-11-28 .Mendozite,, retrieved 2009-11-28 .
  6. ^ Tamarugite,, retrieved 2009-11-28 .Tamarugite,, retrieved 2009-11-28 .