Ammonium dihydrogen phosphate

Ammonium dihydrogen phosphate^[1]

Names
IUPAC name ammonium dihydrogen phosphate
Other names monoammonium phosphate
Identifiers
CAS Number	7722-76-1
ChemSpider	22812
EC Number	231-764-5
Jmol interactive 3D	Image
PubChem	24402
InChI InChI=1S/H3N.H3O4P/c;1-5(2,3)4/h1H3;(H3,1,2,3,4) Key: LFVGISIMTYGQHF-UHFFFAOYSA-N InChI=1/H3N.H3O4P/c;1-5(2,3)4/h1H3;(H3,1,2,3,4) Key: LFVGISIMTYGQHF-UHFFFAOYAX
SMILES [O-]P(=O)(O)O.[NH4+]
Properties
Chemical formula	H6NO4P
Molar mass	115.02 g·mol^−1
Appearance	white crystals
Odor	faint acid
Density	1.80 g/cm^3
Melting point	190 °C (374 °F; 463 K)
Solubility in water	40.4 g/100 mL
Solubility	soluble in ethanol insoluble in acetone
Refractive index (nD)	1.525
Structure
Crystal structure	tetragonal
Thermochemistry
Std enthalpy of formation (ΔfH^o298)	−1445.07 kJ/mol
Hazards
NFPA 704	0 1 0
Lethal dose or concentration (LD, LC):
LD50 (Median dose)	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 n_o = 1.522 and n_e = 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]

Uses

MAP is mainly used as a fertilizer, but also as dry fire extinguisher.

References

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). www.mosaicco.com. Retrieved 2015-06-05.
3. IPNI. "Monoammonium Phosphate (MAP)" (PDF). www.ipni.net. 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.