| Sodium aluminium sulfate | |
|---|---|
|
Aluminium sodium bis(sulfate) — water (1:12) |
|
|
Other names
Sodium alum |
|
| Identifiers | |
| CAS number | 10102-71-3, 7784-28-3 (dodecahydrate) |
| ChemSpider | 22972 |
| EC-number | 233-277-3 |
|
|
| Properties[1] | |
| Molecular formula | NaAl(SO4)2·12H2O |
| Molar mass | 458.28 g/mol |
| Appearance | while 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).[2][3] Two other rare mineral forms are known: mendozite (undecahydrate)[4] and tamarugite (hexahydrate).[5]