Ammonium orthomolybdate

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Ammonium orthomolybdate
Ammonium.svg Molybdat-Ion2.svg Ammonium.svg
Other names
Diammonium molybdate
ECHA InfoCard 100.032.741
Molar mass 196.02 g/mol
Appearance white solid
Lethal dose or concentration (LD, LC):
1870 mg/kg (rabbit, oral)
2200 mg/kg (guinea pig, oral)
1600 mg/kg (cat, oral)[1]
120 mg Mo/kg (rat, oral)
120 mg Mo/kg (guinea pig, oral)[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Ammonium orthomolybdate is the inorganic compound with the chemical formula (NH4)2MoO4. It is a white solid that is prepared by treating molybdenum trioxide with aqueous ammonia. Upon heating these solutions, ammonia is lost, to give ammonium heptamolybdate ((NH4)6Mo7O24.4H2O). Ammonium orthomolybdate is used as a corrosion inhibitor and is an intermediate in some schemes to win Mo from its ores.[2]

Chemical reactions[edit]

Heating Ammonium orthomolybdate solid or treatment with acid gives molybdenum trioxide. Such reactions proceed via ammonium dimolybdate. This equilibrium is exploited in the purification of molybdenum from its ores. Aqueous solutions of ammonium orthomolybdate react with hydrogen sulfide to give ammonium tetrathiomolybdate:

(NH4)2MoO4 + 4 H2S → (NH4)2MoS4 + 4 H2O


  1. ^ a b "Molybdenum (soluble compounds, as Mo)". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH). 
  2. ^ Roger F. Sebenik et al. "Molybdenum and Molybdenum Compounds" in Ullmann's Encyclopedia of Chemical Technology 2005; Wiley-VCH, Weinheim. doi:10.1002/14356007.a16_655