ammonium orthomolybdate
{{Chembox
| ImageSize =
| ImageAlt =
| IUPACName =
| OtherNames = Diammonium molybdate
|Section1={{Chembox Identifiers
| CASNo = 13106-76-8
| PubChem = 61578
| ChemSpiderID = 17339732
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 91249
| EC_number = 236-031-3
| StdInChI=1S/Mo.2H3N.4O/h;2*1H3;;;;/q;;;;;2*-1/p+2
| StdInChIKey = APUPEJJSWDHEBO-UHFFFAOYSA-P
| SMILES = [NH4+].O=[Mo]([O-])([O-])=O.[NH4+]}}
|Section2={{Chembox Properties
| Formula = (NH4)2MoO4
| MolarMass = 196.02 g/mol
| Appearance = colorless monoclinic crystals
| Density = 2.276 g/cm3
| MeltingPt = decomposes upon heating
| BoilingPtC =
| Solubility = soluble
| SolubleOther = insoluble in alcohol and liquid ammonia
}}
|Section3={{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt =
| LDLo = 120 mg Mo/kg (rat, oral)
120 mg Mo/kg (guinea pig, oral){{IDLH|moly-mo|Molybdenum (soluble compounds, as Mo)}}
| LD50 = 1870 mg/kg (rabbit, oral)
2200 mg/kg (guinea pig, oral)
1600 mg/kg (cat, oral)
}}
}}
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).
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.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}} 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{{cite journal |last1=Murakami |first1=Masahiko |last2=Hirano |first2=Masaya |last3=Shibahara |first3=Toshiaki |last4=Kubota |first4=Toshio |title=Speciation of Inorganic Arsenic in Groundwater as Molybdoarsenate by On-Site Solid-Phase Extraction and Graphite Furnace Atomic Absorption Spectrometry |journal=Analytical Letters |date=18 February 2016 |volume=49 |issue=13 |pages=2119–2131 |doi=10.1080/00032719.2015.1135932|s2cid=100305249 }}