Ammonium dihydrogen phosphate

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Ammonium dihydrogen phosphate[1]
Crystals of Ammonium Dihydrogen Phosphate
Ammonium dihydrogen phosphate.png
Ball-and-stick model of the dihydrogenphosphate anion
Ball-andstick model of the ammonium cation
IUPAC name
ammonium dihydrogen phosphate
Other names
monoammonium phosphate
7722-76-1 YesY
3D model (Jmol) Interactive image
ChemSpider 22812 YesY
ECHA InfoCard 100.028.877
EC Number 231-764-5
PubChem 24402
Molar mass 115.02 g·mol−1
Appearance white crystals
Odor faint acid
Density 1.80 g/cm3
Melting point 190 °C (374 °F; 463 K)
40.4 g/100 mL
Solubility soluble in ethanol
insoluble in acetone
−1445.07 kJ/mol
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Lethal dose or concentration (LD, LC):
5750 mg/kg (rat, oral)
Related compounds
Other anions
Ammonium phosphate
Diammonium phosphate
Other cations
Monosodium phosphate
Potassium dihydrogen phosphate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Ammonium dihydrogen phosphate (ADP), also known as monoammonium phosphate (MAP),[2] NH4H2PO4, is formed when a solution of phosphoric acid is added to ammonia until the solution is distinctly acidic. It crystallizes in tetragonal prisms. Monoammonium phosphate is often used in the blending of dry agricultural fertilizers.[3] It supplies soil with the elements nitrogen and phosphorus in a form usable by plants. The compound is also a component of the ABC powder in some dry chemical fire extinguishers. This substance is also supplied in an emerald green, amethyst, or aquamarine crystal growing box kit for children.

Solid monoammonium phosphate shows a dissociation pressure of ammonia of 0.05 mm Hg at 125 °C based on the decomposition reaction as follows:[4]

NH4H2PO4(s) ⇌ NH3(g) + H3PO4(l)

ADP is a widely used crystal in the field of optics due to its birefringence properties. As a result of its tetragonal crystal structure, this material has negative uniaxial optical symmetry with typical refractive indices no = 1.522 and ne = 1.478 at optical wavelengths.[5]

ADP crystals are piezoelectric, a property required in some active sonar transducers (the alternative being transducers that use magnetostriction). In the 1950s ADP crystals largely replaced the quartz and Rochelle salt crystals in transducers because they are easier to work than Quartz and, unlike Rochelle Salt, are not deliquescent.[6]


MAP is mainly used as a fertilizer, but also as dry fire extinguisher. However MAP is also used in children's crystal growing experiment uses.


  1. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. pp. 4–40. ISBN 0-8493-0594-2. 
  2. ^ "Monoammonium Phosphate (MAP)" (PDF). Retrieved 2015-06-05. 
  3. ^ IPNI. "Monoammonium Phosphate (MAP)" (PDF). International Plant Nutrition Institute. Retrieved 21 July 2014. 
  4. ^ John R Van Wazer (1958). Phosphorus And Its Compounds - Volume I: Chemistry. New York: Interscience Publishers, Inc. p. 503. 
  5. ^ Amnon Yariv, Pochi Yeh (1984). Optical Waves in Crystals. Wiley, Inc. 
  6. ^ Willem Hackmann (1984). Seek and Strike: Sonar, Anti-Submarine Warfare and the Royal Navy, 1914–1954. Her Majesty's Stationery Office. ISBN 0-11-290423-8.