Sodium aluminium sulfate

Sodium aluminium sulfate
IUPAC name Aluminium sodium bis(sulfate) — water (1:12)
Other names Sodium alum Soda alum E521
Identifiers
CAS number	10102-71-3,  7784-28-3 (dodecahydrate)
PubChem	24939
ChemSpider	22972
EC-number	233-277-3
Jmol-3D images	Image 1
SMILES [O-]S(=O)(=O)[O-].[O-]S(=O)(=O)[O-].[Na+].[Al+3]
InChI InChI=1S/Al.Na.2H2O4S.12H2O/c;;2*1-5(2,3)4;;;;;;;;;;;;/h;;2*(H2,1,2,3,4);12*1H2/q+3;+1;;;;;;;;;;;;;;/p-4 Key: ZEMWIYASLJTEHQ-UHFFFAOYSA-J InChI=1/Al.Na.2H2O4S.12H2O/c;;2*1-5(2,3)4;;;;;;;;;;;;/h;;2*(H2,1,2,3,4);12*1H2/q+3;+1;;;;;;;;;;;;;;/p-4 Key: ZEMWIYASLJTEHQ-XBHQNQODAL
Properties
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
Solubility in water	208 g/100 ml (15 °C)
Refractive index (nD)	1.4388
Structure
Crystal structure	Cubic, cP96
Space group	Pa3, No. 205
Lattice constant	a = 1221.4 pm
Coordination geometry	Octahedral (Na+) Octahedral (Al3+)
Hazards
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, 100 kPa)
Infobox references

Sodium aluminium sulfate, NaAl(SO₄)₂·12H₂O or Na₂SO₄·Al₂(SO₄)₃·24H₂O, also known as soda alum or sodium alum, is a form of alum used in the acidity regulator of food (E521) as well as in the manufacture of baking powder. It is also a common mordant for the preparation of hematoxylin solutions for staining cell nuclei in histopathology.

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).