Description
Aluminium potassium sulphate extra pure, commonly known as potash alum, is a refined double salt with the formula
KAl(SO
4
)
2
⋅
12
H
2
O
KAl(SO
4
)
2
⋅12H
2
O. It appears as a colorless or white, glassy crystalline solid, highly soluble in water and widely used for its purity in analytical, pharmaceutical, food, and industrial applications.
Chemical Properties and Physical Characteristics
Formula:
KAl(SO
4
)
2
⋅
12
H
2
O
KAl(SO
4
)
2
⋅12H
2
O (dodecahydrate).
CAS Number: 7784-24-9.
Molar Mass: 474.39 g/mol (dodecahydrate).
Appearance: White, crystalline, odorless, slightly sweet and astringent taste.
Density: 1.725 g/cm³.
Solubility: Highly soluble in water; insoluble in alcohol.
Melting Point: Liquefies at 92°C in its own water of crystallization.
pH: Acidic aqueous solution; changes blue litmus to red.
Assay (extra pure): Typically ≥99% with minimal contamination of heavy metals or chloride/iron ions.
Applications
Analytical Reagent: Used in gravimetric and colorimetric analysis in laboratories.
Water Treatment: Acts as a flocculant and coagulant for purifying drinking water.
Food Industry: Utilized as an additive and preservative in pickles, baking, and clarifying agents.
Cosmetics and Medical: Employed in pharmaceutical preparations, antiperspirants, and topical medicinal uses for wound treatment and as an astringent.
Textiles, Dyeing, and Tanning: Used as a mordant in dyeing textiles, for tanning leather, and as a fixative for pigments.
Culinary and Household: Common traditional use as 'fitkari' for domestic water purification, mouth rinses, and as a deodorant.
Other: Research and industrial processes requiring high grades of purity, such as electronics and catalysis.
Technical and Safety Highlights
Crystalline Form: Regular octahedral glassy crystals.
Decomposition: When heated to high temperatures, loses water and decomposes to alumina and potassium sulphate.
Storage: Stable when kept dry; absorbs moisture.
Safety: Generally recognized as safe for handling under standard laboratory and industrial conditions.
Aluminium potassium sulphate extra pure (potash alum) is valued for its consistent purity and versatility across analytical, food, pharmaceutical, water treatment, and textile applications.