Sodium aluminium sulfate is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

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 symbols, ...

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 increase ...

and as a

food additive Food additives are substances added to food to preserve flavor or enhance taste, appearance, or other sensory qualities. Some additives have been used for centuries as part of an effort to preserve food, for example vinegar (pickling), salt (salt ...

. Its official mineral name is alum-Na ( IMA

symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...

: 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 Sodium sulfate (also known as sodium sulphate or sulfate of soda) is the inorganic compound with formula Na2SO4 as well as several related hydrates. All forms are white solids that are highly soluble in water. With an annual production of 6 milli ...

and

aluminium sulfate Aluminium sulfate is a salt with the chemical formula, formula aluminium, Al2sulfate, (SO4)3. It is soluble in water and is mainly used as a Coagulation (water treatment), coagulating agent (promoting particle collision by neutralizing charge) in ...

. An estimated 3000 ton/y (2003) are produced worldwide. The dodecahydrate is known in

mineralogy Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...

as alum-(Na). Two other rare mineral forms are known: mendozite (undecahydrate) and

tamarugite Tamarugite (sodium, Naaluminium, Al(sulfur, Soxygen, O4)2·6hydrogen, H2O) is a colorless monoclinic sulfate mineral. Deposits containing tamarugite are geographically dispersed with occurrences of the mineral on all seven continents (Antarctica ...

(hexahydrate).

Uses

In the US, some brands combine sodium aluminum sulfate with

sodium bicarbonate Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation ( Na+) and a bicarbonate anion ( HCO3−) ...

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 sol ...

in formulations of double acting

. Kawahara et al 1994 noted that aluminum is “a suspected risk factor in

Alzheimer's disease Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...

” and that “aluminum directly influences the process of Alzheimer′s disease”. Sodium alum is also used as an

acidity regulator Acidity regulators, or pH control agents, are food additives used to change or maintain pH (acidity or basicity). They can be organic or mineral acids, bases, neutralizing agents, or buffering agents. Typical agents include the following acids ...

in food, with

E number E numbers ("E" stands for "Europe") are codes for substances used as food additives, including those found naturally in many foods such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...

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 h ...

solutions for

staining Staining is a technique used to enhance contrast in samples, generally at the microscopic level. Stains and dyes are frequently used in histology (microscopic study of biological tissues), in cytology (microscopic study of cells), and in the ...

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, h ...

histopathology Histopathology (compound of three Greek words: ''histos'' "tissue", πάθος ''pathos'' "suffering", and -λογία '' -logia'' "study of") refers to the microscopic examination of tissue in order to study the manifestations of disease. Spe ...

. 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