If you work with aluminum sulfate or “alum” in one specific industrial operation, you might not know around its numerous other uses or the properties that make it so useful for industrial, medical and also consumer applications. Us think alum is among the unsung heroes that the chemistry world, and we’ve created this post so you deserve to learn much more about aluminum sulfate composition and also usage.

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Chemical Composition

Aluminum sulfate exists together white, lustrous crystals, granules, or powder. In nature, it exists as the mineral alunogenite. Aluminium sulfate is sometimes referred to as alum or papermaker’s alum, however, the name “alum” is much more commonly and properly used for any twin sulfate salt v the share formula XAl(SO4)2·12H2O, where X is a monovalent cation such together potassium or ammonium (5). Aluminum sulfate has an action comparable to that of alum however is an ext stringent (2). Aluminum sulfate is an aluminum salt created of aluminum, sulfur, and oxygen, three numerous elements. Its molecule formula is Al2(SO4)3 or Al2S3O12 or Al2O12S3.


Chemical formulaAl2(SO4)3
Molar mass342.15 g/mol (anhydrous) 666.44 g/mol (octadecahydrate)
AppearanceWhite crystalline solid Hygroscopic
Density2.672 g/cm3 (anhydrous) 1.62 g/cm3(octadecahydrate)
Melting point770 °C (1,420 °F; 1,040 K) (decomposes, anhydrous) 86.5 °C (octadecahydrate)
Solubility in water31.2 g/100 mL (0 °C) 36.4 g/100 mL (20 °C) 89.0 g/100 mL (100 °C)
Solubilityslightly soluble in alcohol, dilute mineral acids
Acidity (pKa)3.3-3.6
Magnetic susceptibility (χ)-93.0·10−6 cm3/mol
Refractive index(nD)1.47<1>
Thermodynamic dataPhase behaviour: solid–liquid–gas
Std enthalpy of formation (ΔfH⦵298)-3440 kJ/mol

Where Is Aluminum Sulfate Used?

Water treatment Applications


Because aluminum sulfate is exceptionally acidic, it’s sometimes included to an extremely alkaline soils come balance the pH because that plants. As soon as aluminum sulfate comes into contact with water, it creates aluminum hydroxide and a lot diluted sulfuric acid solution, which transforms the soil acidity. Gardeners who plant hydrangeas apply this building to change the flower shade (blue or pink) of the hydrangeas due to the fact that this tree is very sensitive to floor pH (6).

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Need Aluminum Sulfate for your Application?

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