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 ammoniaNH 3 and molten phosphoric acidH 3PO 4.[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]
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 pentoxideP 2O 5, or 27% of elemental phosphorus.
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]
Monoammonium phosphate crystals are piezoelectric, a property required in some active sonartransducers (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]
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 in guano deposits.[13][14] A related compound, that is the monohydrogen counterpart, is the even more scarce phosphammite.[15][16]
^
Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. pp. 4–40. ISBN0-8493-0594-2.
^ abcDejun 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. doi:10.1021/acs.jced.5b00224
^ abcAmnon Yariv, Pochi Yeh (1984). Optical Waves in Crystals. Wiley, Inc.
^ abWillem Hackmann (1984). Seek and Strike: Sonar, Anti-Submarine Warfare and the Royal Navy, 1914–1954. Her Majesty's Stationery Office. ISBN0-11-290423-8.
^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
^John R Van Wazer (1958). Phosphorus And Its Compounds - Volume I: Chemistry. New York: Interscience Publishers, Inc. p. 503.