Ammonium dihydrogen phosphate

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.

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

A solution of stoichiometric monoammonium phosphate is acidic (pH 4.7 at 0.1% concentration, 4.2 at 5%).

Preparation

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

: + →

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 , 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 and at optical wavelengths.

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.

Toys

Being relatively non-toxic, 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. A related compound, that is the monohydrogen counterpart, is the even more scarce phosphammite.

References

References

1. Chemical Book: "[http://www.chemicalbook.com/ChemicalProductProperty_EN_CB6131092.htm Ammonium dihydrogen phosphate]". Accessed on 2018-08-14.
2. National Bureau of Standards. Selected Values of Chemical Thermodynamic Properties. Technical note 270-3. 1968 [https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote270-3.pdf]
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7. Willem Hackmann. (1984). "Seek and Strike: Sonar, Anti-Submarine Warfare and the Royal Navy, 1914–1954". Her Majesty's Stationery Office.
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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. {{doi. 10.1021/jf60142a002
10. John R Van Wazer. (1958). "Phosphorus And Its Compounds - Volume I: Chemistry". Interscience Publishers, Inc.
11. Haifa Chemicals Ltd.: "[http://www.plantproducts.com/us/images/map_haifa_product_sheet.pdf Mono-Ammonium Phosphate 12-61-0] {{Webarchive. link. (15 October 2022 ". Product fact sheet, accessed on 2018-08-13.)
12. Martin Bäckman, Martin Gunnarsson, Linnea Kollberg, Martin Müller, and Simon Tallvod (2016): "[https://www.chemeng.lth.se/ket050/Finalreport2016/Yara.pdf Production of Monoammonium Phosphate at Yara AB] {{Webarchive. link. (18 November 2017 ". Technical Report, Lund University.)
13. "Biphosphammite".
14. (21 March 2011). "List of Minerals".
15. "Phosphammite".
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