Ammonium dihydrogen phosphate

Ammonium dihydrogen phosphate

Crystals of Ammonium Dihydrogen Phosphate
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Names
IUPAC name ammonium dihydrogen phosphate
Other names monoammonium phosphate
Identifiers
CAS Number	7722-76-1 Y
ChemSpider	22812 Y
EC Number	231-764-5
Jmol 3D model	Interactive image
PubChem	24402
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
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/cm3
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 (ΔfHo298)	−1445.07 kJ/mol
Vapor pressure	{{{value}}}
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), 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 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:

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.

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.

Uses

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