Monoammonium Phosphate (CAS 7722-76-1)

Ammonium dihydrogen phosphate (ADP), also known as monoammonium phosphate (MAP) is a chemical compound with the chemical formula (NH4)(H2PO4). ADP is a major ingredient of agricultural fertilizers and some fire extinguishers. It also has significant uses in optics and electronics.

Monoammonium phosphate is soluble in water and crystallizes from it as the anhydrous salt in the tetragonal system, as elongated prisms or needles. It is practically insoluble in ethanol.

Solid monoammonium phosphate can be considered stable in practice for temperatures up to 200 °C, when it decomposes into gaseous ammonia NH3 and molten phosphoric acid H3PO4. At 125 °C the partial pressure of ammonia is 0.05 mm Hg.

A solution of stoichometric monoammonium phosphate is acidic (pH 4.7 at 0.1% concentration, 4.2 at 5%).