| Aluminium sulfate |
 |
| General |
| Systematic name |
Aluminium sulfate
hexadecahydrate |
| Other names |
Cake alum
Filter alum
Papermaker's alum
alumogenite
Aluminum sulfate
Aluminium sulphate |
| Molecular formula |
Al2(SO4)3·16H2O |
| Molar mass |
630.40 g/mol |
| Appearance |
white crystalline solid |
| CAS number |
[16828-11-8] |
| EINECS number |
233-135-0 |
| Properties |
| Density and phase |
2.71 g/cm3, solid |
| Solubility in water |
31.3 g/100 ml (0 °C) |
| In ethanol |
Slightly soluble (anh.)
Insoluble (hydrate) |
| Melting point |
770°C decomp. |
| Structure |
| Coordination geometry |
? |
| Crystal structure |
monoclinic (hydrate) |
| Safety data |
| PEL-TWA (OSHA) |
— |
| RTECS number |
BD1700000 |
| Supplementary data page |
| Structure & properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour
Solid, liquid, gas |
| Spectral data |
UV, IR, NMR, MS |
| Related compounds |
| Other cations |
Gallium sulfate
Magnesium sulfate |
| Related compounds |
See Alum |
Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)
|
Aluminium sulfate is a widely used industrial chemical. It is sometimes incorrectly referred to as alum, as it is closely related to this group of compounds. It occurs naturally as the mineral alunogenite. It is frequently used in the purification of drinking water supplies, and also in paper manufacturing.
Aluminium sulfate is rarely, if ever, encountered as the anhydrous salt. It forms a number of different hydrates, of which the hexadecahydrate is the most common.
It can also be very effective at killing Spanish slugs.
Preparation
Aluminium sulfate may be made by dissolving aluminium hydroxide, Al(OH)3, in sulfuric acid, H2SO4:
2Al(OH)3 + 3H2SO4 + 10H2O → Al2(SO4)3·16H2O
Uses
Aluminium is used in water purification and as a mordant in dyeing and printing textiles. In water purification, it adsorbs impurities which are removed as the particulate settles to the bottom of the container.
When dissolved in a large amount of neutral or slightly-alkaline water, aluminium sulfate produces a gelatinous precipitate of aluminium hydroxide, Al(OH)3. In dyeing and printing cloth, the gelatinous precipitate helps the dye adhere to the clothing fibers by rendering the pigment insoluble.
Aluminium sulfate is the active ingredient of some anti-perspirants; however, beginning in 2005 the US Food and Drug Administration no longer recognized it as a wetness reducer.
It is also used in styptic pencils.
See also
- Camelford, a town in Cornwall (UK) where the local water supplies were accidentally contaminated with aluminium sulfate.
References
Suppliers
External links
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