 | |
| Names | |
|---|---|
| IUPAC name Aluminium sodium bis(sulfate) — water (1:12) | |
Other names
| |
| Identifiers | |
| |
3D model (JSmol) | |
| ChemSpider | |
| ECHA InfoCard | 100.030.239 |
| EC Number |
|
| E number | E521(acidity regulators, ...) |
| UNII |
|
| |
| |
| Properties[1] | |
| 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) |
| 208 g/100 ml (15 °C) | |
Refractive index (nD) | 1.4388 |
| Structure[2] | |
| Cubic,cP96 | |
| Pa3, No. 205 | |
a = 1221.4 pm | |
| Octahedral (Na+) Octahedral (Al3+) | |
| Hazards | |
| Flash point | non-flammable |
| Related compounds | |
Othercations | Ammonium aluminium sulfate Potassium aluminium sulfate |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Sodium aluminium sulfate is theinorganic compound with thechemical formula NaAl(SO4)2·12H2O (sometimes written Na2SO4·Al2(SO4)3·24H2O). Also known assoda alum,sodium alum, orSAS, this white solid is used in the manufacture ofbaking powder and as afood additive. Its official mineral name isalum-Na (IMAsymbol: Aum-Na[3]).
Like itspotassium analog, sodium aluminum sulfate crystallizes as thedodecahydrate in the classicalcubic alum structure.
Sodium alum is very soluble in water, and is extremely difficult to purify. In the preparation of this salt, it is preferable to mix the component solutions in the cold, and to evaporate them at a temperature not exceeding 60 °C. 100 parts of water dissolve 110 parts of sodium alum at 0 °C, and 51 parts at 16 °C.[4]
Sodium aluminum sulfate is produced by combiningsodium sulfate andaluminium sulfate. An estimated 3000 ton/y (2003) are produced worldwide.
The dodecahydrate is known inmineralogy asalum-(Na).[5][6] Two other rare mineral forms are known:mendozite (undecahydrate)[7] andtamarugite (hexahydrate).[8]
In the US, some brands combine sodium aluminum sulfate withsodium bicarbonate andmonocalcium phosphate in formulations of double actingbaking powder.[9]
Sodium alum is also used as anacidity regulator in food, withE numberE521.
Sodium alum is also a commonmordant for the preparation ofhematoxylin solutions forstainingcell nuclei inhistopathology.[citation needed]
It is also used as aflocculant in water treatment and disinfection, but its relatively crude, caustic action makes it more suitable for industrial applications.[10]
This article incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Alum".Encyclopædia Britannica. Vol. 1 (11th ed.). Cambridge University Press. pp. 766–767.