Sodium aluminum sulfate

Sodium aluminium sulfate
Names
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)
3D model (Jmol)	Interactive image
ChemSpider	22972
ECHA InfoCard	100.030.239
EC Number	233-277-3
E number	E521 (acidity regulators, ...)
PubChem CID	24939
UNII	0CM6A697VV^Y
InChI InChI=1S/Al.Na.2H2O4S.12H2O/c;;21-5(2,3)4;;;;;;;;;;;;/h;;2(H2,1,2,3,4);121H2/q+3;+1;;;;;;;;;;;;;;/p-4 Key: ZEMWIYASLJTEHQ-UHFFFAOYSA-J InChI=1/Al.Na.2H2O4S.12H2O/c;;21-5(2,3)4;;;;;;;;;;;;/h;;2(H2,1,2,3,4);121H2/q+3;+1;;;;;;;;;;;;;;/p-4 Key: ZEMWIYASLJTEHQ-XBHQNQODAL
SMILES [O-]S(=O)(=O)[O-].[O-]S(=O)(=O)[O-].[Na+].[Al+3]
Properties
Chemical 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 (n_D)	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
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.

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).

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

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.

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