Physical Properties
Colorless, monoclinic crystal; density 2.276 g/cm3; decomposes on heating; soluble in water (decomposes); also soluble in acid; insoluble in alcohol and liquid ammonia.
Uses
Ammonium molybdates are used to prepare high purity grade molybdenum metal powder, sheet, or wire; for colorimetric analysis of phosphates and arsenates; for decorating ceramics; and as catalysts.
Preparation
Ammonium molybdate is prepared by treating molybdenum oxide with excess ammonia in an aqueous solution. The crystals are obtained after evaporation of water.
MoO3 + 2NH3 + H2O → (NH4)2MoO4
Reactions
Decomposes on heating or on treatment with alkalies; reacts with lead chloride and other metal salts to form their metal molybdates:
(NH4)2MoO4 + PbCl2 → PbMoO4 + 2NH4Cl
Reacts with phosphates or arsenates to form ammonium phosphomolybdate (NH4)3PO4•12MoO3, or ammonium arsenomolybdate, (NH4)3AsO4•12MoO3.
Chemical Properties
Ammonium heptamolybdate is an odourless crystalline compound ranging in colour from white to yellow-green. It is usually encoutered as the tetrahydrate, whose chemical formula is (NH4)6Mo7O24·4H2O. It is often referred to simply as ammonium molybdate, although this name can also refer to ammonium orthomolybdate, (NH4)2MoO4, and several other species.
General Description
White to greenish-yellow solid. Sinks and mixes with water.
Air & Water Reactions
Water soluble.
Reactivity Profile
Salts, basic, such as Hexaammonium molybdate , are generally soluble in water. The resulting solutions contain moderate concentrations of hydroxide ions and have pH's greater than 7.0. They react as bases to neutralize acids. These neutralizations generate heat, but less or far less than is generated by neutralization of the bases in reactivity group 10 (Bases) and the neutralization of amines. They usually do not react as either oxidizing agents or reducing agents but such behavior is not impossible.
Health Hazard
Inhalation causes irritation of nose and throat. Contact with eyes causes irritation.
Fire Hazard
Special Hazards of Combustion Products: Toxic oxides of nitrogen may form in fire.
Flammability and Explosibility
Not classified
Agricultural Uses
Ammonium molybdate, (NH
4)
6MO
7O
24·2H
2O is an
important molybdenum fertilizer. It is an ammonium salt
of molybdic acid and contains about 50% molybdenum.
Ammonium molybdate is generally mixed with NPK
fertilizers, depending on the crop requirement (generally
50 to l000 gm per ha). The fertilizer is also applied as a
foliar spray, but coating or soaking seeds with
ammonium molybdate is the easiest method of
application, which requires very little fertilizer.
Safety Profile
Mutation data reported. Whenheated to decomposition it emits toxic vapors of Mo andNH3.
