Sodium aluminium sulfate is the inorganic compound with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...

NaAl(SO₄)₂·12H₂O (sometimes written Na₂SO₄·Al₂(SO₄)₃·24H₂O). Also known as soda alum, sodium alum, or SAS, this white solid is used in the manufacture of

baking powder Baking powder is a dry chemical leavening agent, a mixture of a carbonate or bicarbonate and a weak acid. The base and acid are prevented from reacting prematurely by the inclusion of a buffer such as cornstarch. Baking powder is used to increas ...

and as a food additive. Its official mineral name is alum-Na ( IMA symbol: Aum-Na).

Properties

Like its potassium analog, sodium aluminum sulfate crystallizes as the dodecahydrate in the classical cubic 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.

Production and natural occurrence

Sodium aluminum sulfate is produced by combining sodium sulfate and aluminium sulfate. An estimated 3000 ton/y (2003) are produced worldwide. The dodecahydrate is known in mineralogy as alum-(Na). Two other rare mineral forms are known: mendozite (undecahydrate) and tamarugite (hexahydrate).

Uses

In the US, some brands combine sodium aluminum sulfate with sodium bicarbonate and

monocalcium phosphate Monocalcium phosphate is an inorganic compound with the chemical formula Ca(H2PO4)2 ("AMCP" or "CMP-A" for anhydrous monocalcium phosphate). It is commonly found as the monohydrate ("MCP" or "MCP-M"), Ca(H2PO4)2·H2O. Both salts are colourless ...

in formulations of double acting

. Kawahara et al 1994 noted that aluminum is “a suspected risk factor in Alzheimer's disease” and that “aluminum directly influences the process of Alzheimer′s disease”. Sodium alum is also used as an acidity regulator in food, with E number E521. Sodium alum is also a common

mordant A mordant or dye fixative is a substance used to set (i.e. bind) dyes on fabrics by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains in ...

for the preparation of

hematoxylin Haematoxylin or hematoxylin (), also called natural black 1 or C.I. 75290, is a compound extracted from heartwood of the logwood tree ('' Haematoxylum campechianum'') with a chemical formula of . This naturally derived dye has been used as a ...

solutions for staining

cell nuclei The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, ha ...

in histopathology. It is also used as a flocculant in water treatment and disinfection, but its relatively crude, caustic action makes it more suitable for industrial applications.

References

Aluminium compounds Sodium compounds Sulfates Double salts E-number additives {{inorganic-compound-stub