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Aluminium sulphate

Aluminium sulfate
Aluminium sulfate hexadecahydrate
Names
IUPAC name
Aluminium sulfate
Other names
Cake alum
Filter alum
Papermaker's alum
Alunogenite
aluminum salt (3:2)
Identifiers
10043-01-3 YesY
7784-31-8 (octadecahydrate) N
3D model (Jmol) Interactive image
ChemSpider 23233 YesY
ECHA InfoCard 100.030.110
EC Number 233-135-0
E number E520 (acidity regulators, ...)
PubChem 24850
RTECS number BD1700000
UNII I7T908772F YesY
Properties
Al2(SO4)3
Molar mass 342.15 g/mol (anhydrous)
666.42 g/mol (octadecahydrate)
Appearance white crystalline solid
hygroscopic
Density 2.672 g/cm3 (anhydrous)
1.62 g/cm3 (octadecahydrate)
Melting point 770 °C (1,420 °F; 1,040 K) (decomposes, anhydrous)
86.5 °C (octadecahydrate)
31.2 g/100 mL (0 °C)
36.4 g/100 mL (20 °C)
89.0 g/100 mL (100 °C)
Solubility slightly soluble in alcohol, dilute mineral acids
Acidity (pKa) 3.3-3.6
-93.0·10−6 cm3/mol
1.47
Structure
monoclinic (hydrate)
Thermochemistry
-3440 kJ/mol
Hazards
Safety data sheet See: data page
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
US health exposure limits (NIOSH):
PEL (Permissible)
none
REL (Recommended)
2 mg/m3
IDLH (Immediate danger)
N.D.
Related compounds
Other cations
Gallium sulfate
Magnesium sulfate
Related compounds
See Alum
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Thermodynamic
data
Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Aluminium sulfate is a chemical compound with the formula Al2(SO4)3. It is soluble in water and is mainly used as a flocculating agent (causing contaminating particles to clump into larger, more easily trapped particles) in the purification of drinking water and waste water treatment plants, and also in paper manufacturing.

Aluminium sulfate is sometimes referred to as a type of alum. Alums are double sulfate salts, with the formula AM(SO
4
)
2
·12H
2
O
, where A is a monovalent cation such as potassium or ammonium and M is a trivalent metal ion such as aluminium. The anhydrous form occurs naturally as a rare mineral millosevichite, found e.g. in volcanic environments and on burning coal-mining waste dumps. Aluminium sulfate is rarely, if ever, encountered as the anhydrous salt. It forms a number of different hydrates, of which the hexadecahydrate Al2(SO4)3•16H2O and octadecahydrate Al2(SO4)3•18H2O are the most common. The heptadecahydrate, whose formula can be written as [Al(H2O)6]2(SO4)3•5H2O, occurs naturally as the mineral alunogen.

Aluminium sulfate may be made by adding aluminium hydroxide, Al(OH)3, to sulfuric acid, H2SO4:


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