Ammonium orthomolybdate

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

Names
Other names Diammonium molybdate
Identifiers
CAS Number	13106-76-8
3D model (JSmol)	Interactive image
ChEBI	CHEBI:91249 Y
ChemSpider	17339732
ECHA InfoCard	100.032.741
EC Number	236-031-3
PubChem CID	61578
CompTox Dashboard (EPA)	DTXSID5051654
InChI InChI=1S/Mo.2H3N.4O/h;2*1H3;;;;/q;;;;;2*-1/p+2 Key: APUPEJJSWDHEBO-UHFFFAOYSA-P
SMILES [NH4+].O=[Mo]([O-])([O-])=O.[NH4+]
Properties
Chemical formula	(NH4)2MoO4
Molar mass	196.02 g/mol
Appearance	colorless monoclinic crystals
Density	2.276 g/cm3
Melting point	decomposes upon heating
Solubility in water	soluble
Solubility	insoluble in alcohol and liquid ammonia
Hazards
Lethal dose or concentration (LD, LC):
LD50 (median dose)	1870 mg/kg (rabbit, oral) 2200 mg/kg (guinea pig, oral) 1600 mg/kg (cat, oral)[1]
LDLo (lowest published)	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

Uses

Ammonium orthomolybdate is used as a corrosion inhibitor and is an intermediate in some schemes as an intermediate to extract molybdenum from its ores.^[2] 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 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

It reacts with arsenic acid upon heating to form a canary yellow precipitate of ammonium α-Keggin molybdoarsenate.

(NH₄)₂MoO₄ + H₃AsO₄ → (NH₄)₂[As(Mo₃O₁₀)₄] + 21 NH₄NO₃ + 12 H₂O^[3]