Sodium aluminium sulfate

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, sodium alum, or SAS, this white solid is used in the manufacture of baking powder and as a food additive.

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.

Sodium aluminum sulfate is produced by combining sodium sulfate and aluminium sulfate. An estimated 3000 ton/y are (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).

In the US, sodium aluminum sulfate is combined with sodium bicarbonate and monocalcium phosphate in typical formulations of double acting baking powder. Sodium alum acts as an acid which is activated at baking temperatures. The aluminum content of these baking powders is seen by some consumers as a health concern.

This page was last edited on 8 February 2018, at 22:39.
Reference: under CC BY-SA license.

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