Diammonium phosphate

Diammonium phosphate
Diammonium phosphate[1]
CAS number 7783-28-0 YesY
PubChem 24540
ChemSpider 22946 YesY
Jmol-3D images Image 1
Molecular formula (NH4)2HPO4
Molar mass 132.07 g/mol
Appearance white powder
Density 1.619 g/cm3
Melting point

155 ºC decomp.

Solubility in water 57.5 g/100 mL (10 ºC)
106.7 g/100 mL (100 °C)
Solubility insoluble in alcohol, acetone and liquid ammonia
Refractive index (nD) 1.52
Std enthalpy of
-1566.91 kJ/mol
EU Index Not listed
NFPA 704
NFPA 704.svg
Flash point Non-flammable
Related compounds
Other anions Monoammonium phosphate
Triammonium phosphate
Other cations Disodium phosphate
Dipotassium phosphate
Related compounds Ammonium nitrate
Ammonium sulfate
 N phosphate (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Diammonium phosphate (DAP) (chemical formula (NH4)2HPO4, IUPAC name diammonium hydrogen phosphate) is one of a series of water-soluble ammonium phosphate salts which can be produced when ammonia reacts with phosphoric acid. Solid diammonium phosphate shows a dissociation pressure of ammonia as given by the following expression and equation:[2]

(NH4)2HPO4(s) is in equilibrium with NH3(g) + NH4H2PO4(s)
log PmmHg = -3063 / T + 175 log T + 3.3


P = the resultant dissociation pressure of ammonia
T = absolute temperature (K)

At 100ºC, the dissociation pressure of diammonium phosphate is approximately 5 mmHg.[3]


DAP is used as a fertilizer. When applied as plant food, it temporarily increases the soil pH, but over a long term the treated ground becomes more acidic than before upon nitrification of the ammonium. It is incompatible with alkaline chemicals because its ammonium ion is more likely to convert to ammonia in a high-pH environment.

DAP can be used as a fire retardant. It lowers the combustion temperature of the material, decreases maximum weight loss rates, and causes an increase in the production of residue or char.[4] These are important effects in fighting wildfires as lowering the pyrolysis temperature and increasing the amount of char formed reduces that amount of available fuel and can lead to the formation of a firebreak. It is the largest component of some popular commercial firefighting products.[5]

DAP is also used as a yeast nutrient in winemaking and brewing mead; as an additive in some brands of cigarettes purportedly as a nicotine enhancer; to prevent afterglow in matches, in purifying sugar; as a Flux for soldering tin, copper, zinc and brass; and to control precipitation of alkali-soluble and acid-insoluble colloidal dyes on wool. [1]

External links


  1. ^ a b Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
  2. ^ John R Van Wazer (1958). Phosphorus And Its Compounds - Volume I: Chemistry. New York: Interscience Publishers, Inc. p. 503. 
  3. ^ McKetta Jr, John J., ed (1990). Encyclopedia of Chemical Processing and Design (Chemical Processing and Design Encyclopedia). New York: Marcel Dekker, Inc. p. 478. ISBN 0824724852. http://books.google.com/?id=z2NLRf0ROx0C&lpg=PA478&dq=%22dissociation%20pressure%22%20ammonium%20phosphate&pg=PA478#v=onepage&q=%22dissociation%20pressure%22%20ammonium%20phosphate. 
  4. ^ George, C.W.; Susott, R.A. (April 1971). "Effects of Ammonium Phosphate and Sulfate on the Pyrolysis and Combustion of Cellulose". Research Paper INT-90 (Intermountain Forest and Range Experiment Station: USDA Forest Service). http://openlibrary.org/b/OL16022833M/Effects_of_ammonium_phosphate_and_sulfate_on_the_pyrolysis_and_combustion_of_cellulose 
  5. ^ Phos-Chek MSDS, Phos-Chek website

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Look at other dictionaries:

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  • diammonium phosphate — noun : ammonium phosphate * * * /duy euh moh nee euhm, duy /, Chem. a white, crystalline, water soluble compound, (NH4)2HPO4, used as fertilizer, in fire extinguishers, etc. [DI 1 + AMMONIUM] …   Useful english dictionary

  • diammonium phosphate — noun Date: circa 1929 a white crystalline compound (NH4)2HPO4 used especially as a fertilizer and as a fire retardant …   New Collegiate Dictionary

  • diammonium phosphate — /duy euh moh nee euhm, duy /, Chem. a white, crystalline, water soluble compound, (NH4)2HPO4, used as fertilizer, in fire extinguishers, etc. [DI 1 + AMMONIUM] * * * …   Universalium

  • Ammonium phosphate — For other uses, see Ammonium phosphate (disambiguation). Ammonium phosphate[1] …   Wikipedia

  • ammonium phosphate — noun : a phosphate of ammonium made by reaction of ammonia and phosphoric acid: as a. : the white crystalline primary phosphate NH4H2PO4 or sometimes a commercial mixture of this with ammonium sulfate, used chiefly as a fertilizer and as a fire… …   Useful english dictionary

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