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| Names | |
|---|---|
| IUPAC name Ammonium dihydrogen phosphate | |
| Other names Monoammonium phosphate | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider |
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| ECHA InfoCard | 100.028.877 |
| EC Number |
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| E number | E342(i)(antioxidants, ...) |
| UNII | |
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| Properties | |
| H6NO4P | |
| Molar mass | 115.025 g·mol−1 |
| Appearance | white crystals |
| Odor | none |
| Density | 1.80 g/cm3 |
| Melting point | 190 °C (374 °F; 463 K) |
| (g/dL) 28 (10 °C) 36 (20 °C) 44 (30 °C) 56 (40 °C) 66 (50 °C) 81 (60 °C) 99 (70 °C) 118 (80 °C) 173 (100 °C)[2][3] | |
| Solubility | insoluble inethanol[2] insoluble inacetone |
Refractive index (nD) | 1.525 |
| Structure | |
| tetragonal | |
| Thermochemistry | |
Std enthalpy of formation(ΔfH⦵298) | −1445.07 kJ/mol[4] |
| Hazards | |
| GHS labelling: | |
 | |
| Warning | |
| H319 | |
| P261,P264,P271,P280,P302+P352,P304+P340,P305+P351+P338,P312,P321,P332+P313,P337+P313,P362,P403+P233,P405,P501 | |
| NFPA 704 (fire diamond) | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 5750 mg/kg (rat, oral) |
| Related compounds | |
Otheranions | Ammonium phosphate Diammonium phosphate |
Othercations | Monosodium phosphate Potassium dihydrogen phosphate |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Ammonium dihydrogen phosphate (ADP), also known asmonoammonium phosphate (MAP)[5] is achemical compound with thechemical formula (NH4)(H2PO4). ADP is a major ingredient of agriculturalfertilizers[6] anddry chemical fire extinguishers.[7] It also has significant uses inoptics[8] andelectronics.[9]
Monoammonium phosphate is soluble in water and crystallizes from it as the anhydroussalt in thetetragonal system, as elongatedprisms or needles.[8] It is practically insoluble inethanol.[2]
Solid monoammonium phosphate can be considered stable in practice for temperatures up to 200 °C, when it decomposes into gaseousammoniaNH
3 and moltenphosphoric acidH
3PO
4.[10] At 125 °C thepartial pressure of ammonia is 0.05 mm Hg.[11]
A solution of stoichometric monoammonium phosphate is acidic (pH 4.7 at 0.1% concentration, 4.2 at 5%).[12]
Monoammonium phosphate is industrially prepared by theexothermic reaction of phosphoric acid and ammonia in the correct proportions:[13]
Crystalline MAP then precipitates.
The largest use of monoammonium phosphate by weight is in agriculture, as an ingredient of fertilizers. It suppliessoil with the elementsnitrogen andphosphorus in a form usable by plants. ItsNPK label is 12-61-0 (12-27-0), meaning that it contains 12% by weight of elemental nitrogen and (nominally) 61% ofphosphorus pentoxideP
2O
5, or 27% of elemental phosphorus.
The compound is also a component of theABC powder in some dry chemicalfire extinguishers.
Monoammonium phosphate is a widely used crystal in the field of optics due to itsbirefringence properties. As a result of its tetragonal crystal structure, this material has negative uniaxial optical symmetry with typical refractive indicesno = 1.522 andne = 1.478 at optical wavelengths.[8]
Monoammonium phosphate crystals arepiezoelectric, a property required in some activesonartransducers (the alternative being transducers that usemagnetostriction). In the 1950s ADP crystals largely replaced thequartz andRochelle salt crystals in transducers because they are easier to work than quartz and, unlike Rochelle salt, are notdeliquescent.[9]
Being relatively non-toxic[citation needed], MAP is also a popular substance for recreational crystal growing, being sold as toy kits mixed with dyes of various colors.
The compound appears in nature as the rare mineral biphosphammite. It is formed inguano deposits.[14][15] A related compound, that is the monohydrogen counterpart, is the even more scarce phosphammite.[16][17]
