Definition

Noun: 1. A specific inorganic chemical compound: Ammonia alum is a white, crystalline, water-soluble solid. It is a double sulfate salt containing aluminum and ammonium ions. Its chemical formula is often written as NH₄Al(SO₄)₂·12H₂O.

Usage

• Ammonia alum is primarily used as a mordant in dyeing textiles, helping dyes bind to fabric.
• It is used in water purification and wastewater treatment as a coagulating agent.
• It finds use in leather tanning, papermaking, and as an ingredient in some cosmetics and astringents.

Examples

• "The dyer used ammonia alum to fix the vibrant color to the wool."
• "Ammonia alum is an effective and common coagulant in small-scale water treatment plants."
• "The chemical formula for ammonia alum indicates it contains water of crystallization."

Advanced Usage

• In chemistry, ammonia alum is a member of the broader alum family, which are double sulfate salts with the general formula XAl(SO₄)₂·12H₂O, where X is a monovalent cation like potassium, sodium, or ammonium.
• It is distinguished from potassium alum (potash alum), which is another common type.

Variants and Related Words

• Ammonium alum: A fully synonymous name for the same compound.
• Alum: A general term for a class of double sulfate salts. Ammonia alum is one specific type of alum.
• Potassium alum (Potash alum): A related compound where the ammonium ion is replaced by a potassium ion (KAl(SO₄)₂·12H₂O).

Synonyms

• Ammonium aluminum sulfate
• Aluminum ammonium disulfate dodecahydrate (systematic chemical name)

Notes on Meaning

The term ammonia alum refers specifically to the chemical compound containing ammonium (NH₄⁺) and aluminum (Al³⁺) ions. It should not be confused with other alums (like potassium alum) or with aqueous ammonia (NH₃), which is a different substance entirely.

Noun

1. a white crystalline double sulfate of aluminum: the ammonium double sulfate of aluminum