Sodium aluminium sulfate

Sodium aluminium sulfate
IUPAC name
Aluminium sodium bis(sulfate) — water (1:12)
Other names
Sodium alum
Soda alum
7784-28-3 (dodecahydrate)
3D model (Jmol) Interactive image
ChemSpider 22972
ECHA InfoCard 100.030.239
EC Number 233-277-3
E number E521 (acidity regulators, ...)
PubChem 24939
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)
Cubic, cP96
Pa3, No. 205
a = 1221.4 pm
Octahedral (Na+)
Octahedral (Al3+)
Flash point non-flammable
Related compounds
Other cations
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).
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

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.[3]

The classical cubic alum structure is the dodecahydrate, which is known in mineralogy as alum-(Na).[4][5] Two other rare mineral forms are known: mendozite (undecahydrate)[6] and tamarugite (hexahydrate).[7]

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. 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.
  3. 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
  4. 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.
  5. Alum-(Na),, retrieved 2009-11-28.Alum-(Na),, retrieved 2009-11-28.
  6. Mendozite,, retrieved 2009-11-28.Mendozite,, retrieved 2009-11-28.
  7. Tamarugite,, retrieved 2009-11-28.Tamarugite,, retrieved 2009-11-28.

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