Ammonium dihydrogen phosphate

Ammonium dihydrogen phosphate[1]
IUPAC name ammonium dihydrogen phosphate
Other names monoammonium phosphate
Identifiers
CAS number	7722-76-1 Y
ChemSpider	22812 Y
Jmol-3D images	Image 1
SMILES [O-]P(=O)(O)O.[NH4+]
InChI InChI=1S/H3N.H3O4P/c;1-5(2,3)4/h1H3;(H3,1,2,3,4) Y Key: LFVGISIMTYGQHF-UHFFFAOYSA-N Y InChI=1/H3N.H3O4P/c;1-5(2,3)4/h1H3;(H3,1,2,3,4) Key: LFVGISIMTYGQHF-UHFFFAOYAX
Properties
Molecular formula	H6NO4P
Molar mass	115.03 g mol−1
Appearance	white tetragonal crystals
Density	1.80 g/cm3
Melting point	190 °C, 463 K, 374 °F
Solubility in water	40.4 g/100 mL
Hazards
NFPA 704	0 1 0
Thermochemistry
Std enthalpy of formation ΔfHo298	-1445.07 kJ/mol
Related compounds
Other anions	Ammonium phosphate Diammonium phosphate
Other cations	Monosodium phosphate Potassium dihydrogen phosphate
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Ammonium dihydrogen phosphate (ADP), or monoammonium phosphate, 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. It supplies soil with the elements nitrogen and phosphorus in a form which is 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 or aquamarine crystal growing box kit for children.

Solid monoammonium phosphate show a dissociation pressure of ammonia of 0.05 mmHg at 125°C based on the decomposition reaction as follows:^[2]

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 an n_e=1.478 at optical wavelengths.^[3]

ADP crystals are piezoelectric which is 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.^[4]

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. ^ John R Van Wazer (1958). Phosphorus And Its Compounds - Volume I: Chemistry. New York: Interscience Publishers, Inc. p. 503. 
3. ^ Amnon Yariv,Pochi Yeh (1984). Optical Waves in Crystals. Wiley, Inc. 
4. ^ 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.