AMMONIUM MOLYBDATE
Formula : (NH4)2M0O4; MW 196.01 
Ammonium ion forms isopolymolybdates, such as di–, tri–, or heptamolybdates with the molybdate anion. Only the dimolybdate, 
and ammonium heptamolybdate 
[12027–67–7], have commercial applications.
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.
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.
Preparation
Ammonium molybdate is prepared by treating molybdenum oxide with excess ammonia in an aqueous solution. The crystals are obtained after evaporation of water.
Reactions
Decomposes on heating or on treatment with alkalies; reacts with lead chloride and other metal salts to form their metal molybdates:
Reacts with phosphates or arsenates to form
ammonium phosphomolybdate 
or
ammonium arsenomolybdate, 
Chemical Analysis
Elemental composition: H 4.11%, Mo 48.94%, N 14.29%; O 32.65. 
is digested with nitric acid and the molybdenum metal is analyzed by atomic absorption or emission spectrophotometry. It is dissociated to ammonia, which may be measured by titration or by an ion-specific electrode technique (see Ammonia). Ammonium molybdate reacts under acid conditions with dilute orthophosphate solution to form molybdophosphoric acid which, in the presence of vanadium, forms yellow vanadomolybdophosphoric acid; the intensity of the yellow color may be measured by a spectrophotometer at 400 to 490 nm and is proportional to the trace amount of ammonium molybdate.
