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(SO
4)
2·12H
2O (sometimes written Na
2SO
4·Al
2(SO
4)
3·24H
2O). 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
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 ...
.
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
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