Ammonium orthomolybdate is the inorganic compound with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...

(NH₄)₂MoO₄. It is a white solid that is prepared by treating

molybdenum trioxide Molybdenum trioxide describes a family of inorganic compounds with the formula MoO3(H2O)n where n = 0, 1, 2. These compounds are produced on the largest scale of any molybdenum compound. The anhydrous oxide is a precursor to molybdenum metal, an ...

with aqueous ammonia. Upon heating these solutions, ammonia is lost, to give

ammonium heptamolybdate Ammonium heptamolybdate is the inorganic compound whose chemical formula is (NH4)6Mo7O24, normally encountered as the tetrahydrate. A dihydrate is also known. It is a colorless solid, often referred to as ammonium paramolybdate or simply as ammoni ...

((NH₄)₆Mo₇O₂₄·4H₂O).

Uses

Ammonium orthomolybdate is used as a

corrosion inhibitor In chemistry, a corrosion inhibitor or anti-corrosive is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy, that comes into contact with the fluid. The effectiveness ...

and is an intermediate in some schemes to win molybdenum from its ores.Roger F. Sebenik et al. "Molybdenum and Molybdenum Compounds" in Ullmann's Encyclopedia of Chemical Technology 2005; Wiley-VCH, Weinheim. It is also used for decorating ceramics, and for colorimetric analysis of phosphates and arsenates.

Chemical reactions

Heating ammonium orthomolybdate solid or treatment with acid gives

. 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 Ammonium tetrathiomolybdate is the chemical compound with the formula (NH4)2MoS4. This bright red ammonium salt is an important reagent in the chemistry of molybdenum and has been used as a building block in bioinorganic chemistry. The thiometalla ...

: : (NH₄)₂MoO₄ + 4 H₂S → (NH₄)₂MoS₄ + 4 H₂O It reacts with arsenic acid upon heating to form a canary yellow precipitate of ammonium α-Keggin molybdoarsenate. : (NH₄)₂MoO₄ + H₃AsO₄ → (NH₄)₂ s(Mo₃O₁₀)₄+ 21 NH₄NO₃ + 12 H₂O

References

Ammonium compounds Molybdates {{inorganic-compound-stub