Ammonium dihydrogen phosphate

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Ammonium dihydrogen phosphate[1]
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Template:Longitem Template:Chembox Elements/molecular formula
Molar mass Template:Chem molar mass
Appearance white crystals
Odor none
Density 1.80 g/cm3
Melting point Template:Chembox CalcTemperatures
Solubility insoluble in ethanol[2]
insoluble in acetone
Template:Longitem 1.525
Template:Longitem tetragonal
Template:Longitem −1445.07 kJ/mol[4]
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Template:Longitem Ammonium phosphate
Diammonium phosphate
Template:Longitem Monosodium phosphate
Potassium dihydrogen phosphate

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Ammonium dihydrogen phosphate (ADP), also known as monoammonium phosphate (MAP)[5] is a chemical compound with the chemical formula (NH4)(H2PO4). ADP is a major ingredient of agricultural fertilizers[6] and dry chemical fire extinguishers. It also has significant uses in optics[7] and electronics.[8]

Chemical properties

Monoammonium phosphate is soluble in water and crystallizes from it as the anhydrous salt in the tetragonal system, as elongated prisms or needles.[7] It is practically insoluble in ethanol.[2]

Solid monoammonium phosphate can be considered stable in practice for temperatures up to 200 °C, when it decomposes into gaseous ammonia Template:Chem/link and molten phosphoric acid Template:Chem/link.[9] At 125 °C the partial pressure of ammonia is 0.05 mm Hg.[10]

A solution of stoichometric monoammonium phosphate is acidic (pH 4.7 at 0.1% concentration, 4.2 at 5%).[11]

Preparation

Monoammonium phosphate is industrially prepared by the exothermic reaction of phosphoric acid and ammonia in the correct proportions:[12]

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Crystalline MAP then precipitates.

Uses

Agriculture

The largest use of monoammonium phosphate by weight is in agriculture, as an ingredient of fertilizers. It supplies soil with the elements nitrogen and phosphorus in a form usable by plants. Its NPK label is 12-61-0 (12-27-0), meaning that it contains 12% by weight of elemental nitrogen and (nominally) 61% of phosphorus pentoxide Template:Chem/link, or 27% of elemental phosphorus.

Fire extinguishers

The compound is also a component of the ABC powder in some dry chemical fire extinguishers.

Optics

Monoammonium phosphate 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.[7]

Electronics

Monoammonium phosphate 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.[8]

Toys

Being relatively non-toxicScript error: No such module "Unsubst"., MAP is also a popular substance for recreational crystal growing, being sold as toy kits mixed with dyes of various colors.

Natural occurrence

The compound appears in nature as the rare mineral biphosphammite. It is formed in guano deposits.[13][14] A related compound, that is the monohydrogen counterpart, is the even more scarce phosphammite.[15][16]

References

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  1. ↑ Script error: No such module "citation/CS1".
  2. ↑ a b c Dejun Xu, Xing Xiong, Lin Yang, Zhiye Zhang, and Xinlong Wang (2016): "Determination of the Solubility of Ammonium Dihydrogen Phosphate in Water-Ethanol System at Different Temperatures from 283.2 to 343.2 K". Journal of Chemincal Engineering Data, volume 61, issue 1, pages 78–82. Script error: No such module "CS1 identifiers".
  3. ↑ Chemical Book: "Ammonium dihydrogen phosphate". Accessed on 2018-08-14.
  4. ↑ National Bureau of Standards. Selected Values of Chemical Thermodynamic Properties. Technical note 270-3. 1968 [1]
  5. ↑ Script error: No such module "citation/CS1".
  6. ↑ Script error: No such module "citation/CS1".
  7. ↑ a b c Script error: No such module "citation/CS1".
  8. ↑ a b Script error: No such module "citation/CS1".
  9. ↑ G. O. Guerrant and D. E. Brown (196): "Thermal Decomposition of High-Analysis Fertilizers Based on Ammonium Phosphate". Journal of Agricultural and Food Chemistry, volume 13, issue 6, pages 493-497. Script error: No such module "CS1 identifiers".
  10. ↑ Script error: No such module "citation/CS1".
  11. ↑ Haifa Chemicals Ltd.: "Mono-Ammonium Phosphate 12-61-0 Script error: No such module "webarchive".". Product fact sheet, accessed on 2018-08-13.
  12. ↑ Martin Bäckman, Martin Gunnarsson, Linnea Kollberg, Martin Müller, and Simon Tallvod (2016): "Production of Monoammonium Phosphate at Yara AB Script error: No such module "webarchive".". Technical Report, Lund University.
  13. ↑ Script error: No such module "citation/CS1".
  14. ↑ Script error: No such module "citation/CS1".
  15. ↑ Script error: No such module "citation/CS1".
  16. ↑ Script error: No such module "citation/CS1".

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Template:Ammonium salts Template:Phosphates

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