Aluminium sulfate

Aluminium sulfate
Names

IUPAC name Aluminium sulfate
Other names Cake alum Filter alum Papermaker's alum Alunogenite aluminum salt (3:2)
Identifiers
CAS Number	10043-01-3^Y 7784-31-8 (octadecahydrate)^N
3D model (Jmol)	Interactive image
ChemSpider	23233^Y
ECHA InfoCard	100.030.110
EC Number	233-135-0
E number	E520 (acidity regulators, ...)
PubChem	24850
RTECS number	BD1700000
UNII	I7T908772F^Y
InChI InChI=1S/2Al.3H2O4S/c;;31-5(2,3)4/h;;3(H2,1,2,3,4)/q2+3;;;/p-6^Y Key: DIZPMCHEQGEION-UHFFFAOYSA-H^Y InChI=1/2Al.3H2O4S/c;;31-5(2,3)4/h;;3(H2,1,2,3,4)/q2+3;;;/p-6 Key: DIZPMCHEQGEION-CYFPFDDLAS
SMILES [Al+3].[Al+3].[O-]S(=O)(=O)[O-].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O
Properties
Chemical formula	Al₂(SO₄)₃
Molar mass	503.922 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)
Solubility in water	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 (pK_a)	3.3-3.6
Magnetic susceptibility (χ)	-93.0·10⁻⁶ cm³/mol
Refractive index (n_D)	1.47
Structure
Crystal structure	monoclinic (hydrate)
Thermochemistry
Std enthalpy of formation (Δ_fH^o₂₉₈)	-3440 kJ/mol
Hazards
Safety data sheet	See: data page
NFPA 704	0 1 0
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
Structure and properties	Refractive index (n), Dielectric constant (ε_r), etc.
Thermodynamic data	Phase behaviour solid–liquid–gas
Spectral data	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 ^YN ?)
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
2O, 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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