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| 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 | * |
| 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) Chemical infobox | |
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 as a coagulant in the purification of drinking water and waste water treatment plants, 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 as a molluscicide, killing Spanish slugs.
Preparation
Aluminum sulfate may be made by dissolving aluminum hydroxide, Al(OH)3, in sulfuric acid, H2SO4:
2Al(OH)3 + 3H2SO4 + 10H2O → Al2(SO4)3·16H2O
Uses
Aluminum Sulfate is used in water purification and as a mordant in dyeing and printing textiles. In water purification, it causes impurities to coagulate which are removed as the particulate settles to the bottom of the container or more easily filtered.
When dissolved in a large amount of neutral or slightly-alkaline water, aluminum sulfate produces a gelatinous precipitate of aluminum 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.
Aluminum sulfate is sometimes used to reduce the pH of garden soil, as it hydrolyzes to form the aluminum hydroxide precipitate and a dilute sulfuric acid solution.
Aluminum sulfate is the active ingredient of some antiperspirants; 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 aluminum sulfate.
References
External links
Aluminium compounds | Sulfates | Molluscicides | Water treatment
Aluminiumsulfat | Sulfate d'aluminium | 硫酸アルミニウム | Алуминијум сулфат
"Aluminium sulfate"