Ammonium sulfate

Ammonium sulfate, (NH₄)₂SO₄, sometimes known as Mohrs Salt, is a chemical compound commonly used as a fertilizer. Ammonium sulfate is quite acidic and will raise the pH balance of the soil as well as other sulfate compounds such as aluminium sulfate.

Ammonium sulfate is not soluble in alcohol or liquid ammonia. Ammonium sulfate is prepared commercially by reacting ammonia with sulfuric acid (H₂SO₄). In the soil the SO₄ is released and forms sulfuric acid and the ammonia contributes nitrogen.

Ammonium sulfate is prepared commercially from the ammoniacal liquor of gas-works and is purified by recrystallization. It forms large rhombic prisms, has a somewhat saline taste and is easily soluble in water. The aqueous solution on boiling loses some ammonia and forms an acid sulfate. It is used largely as an artificial manure, and also for the preparation of other ammonium salts. It is also a component of the ABC powder in some dry powder fire extinguishers.

In biochemistry, ammonium sulfate precipitation is a common method for concentrating proteins.

Properties of ammonium sulfate

• Appearance: fine white granules or crystals.
• Odor: slight odor of ammonia.
• Solubility: appreciable in water, 41.22 g/100 g water @ 25 °C (77 °F)
• Molecular mass: 132.14 g
• Density: 1.77 g/cm³ @ 50 °C (122 °F)
• pH: 5.5 (0.1 mol/L aqueous solution)
• % Volatiles by volume @ 21 °C (70 °F): 0
• Boiling point: not applicable.
• Melting point: 235 to 280 °C (455 to 536 °F) decomposes.
• Critical Relative Humidity: 81% @ 20°C.
• Nitrogen Content: 21.2%