Ammonium heptamolybdate
IUPAC name	Ammonium docosaoxoheptamolybdate(6–)
Other names	Ammonium molybdate Ammonium paramolybdate (see text)
Identifiers
CAS number	12027-67-7 Y, 12054-85-2 (tetrahydrate)
PubChem	24867009
EC number	234-320-9
Properties
Molecular formula	(NH4)6Mo7O24
Molar mass	1163.9 g/mol 1235.86 g/mol (tetrahydrate)
Appearance	white crystalline solid
Density	2.498 g/cm3
Melting point	~90 ˚C
Solubility in water	43 g/100 ml (tetrahydrate)
Hazards
EU Index	Not listed
Main hazards	Irritant
NFPA 704	0 2 0
Flash point	Non-flammable
Related compounds
Other anions	Ammonium orthomolybdate Ammonium dimolybdate
Other cations	Potassium paramolybdate
Related compounds	Molybdenum(VI) oxide Molybdic acid
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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 as ammonium paramolybdate or simply as ammonium molybdate, although the latter name can also refer to ammonium orthomolybdate, (NH₄)₂MoO₄, and several other species.

[edit] Synthesis

Ammonium paramolybdate is easily prepared by dissolving molybdenumtrioxide in an excess of ammonia (a solution of NH₃ in water), and evaporating the solution at room temperature. While the solution evaporates, the excess of ammonia escapes. This method results in the formation of six-sides prisms of the tetrahydrate of ammonium paramolybdate, which are transparent as water [1].
Solutions of ammoniumparamolybdate react acid. The pH value of a concentrated solution will lie between 5 and 6.

[edit] Uses

• as an analytical reagent to find the presence of phosphates, silicates, arsenates and lead in pigments
• in the production of molybdenum metal and ceramics
• in the preparation of dehydrogenation and desulphurisation catalysts
• in the fixing of metals
• in electroplating
• in fertilizers for crops.
• as a negative stain in biological electron microscopy, typically in the 3-5% (vol/vol) concentration range and in the presence of trehalose [2]; or at saturated concentration to perform cryo-negative staining [3,4].

[edit] References

1. L. Svanberg & H. Struve, J. pr. Ch. 44 [1848], 282; cited in Gmelin's Handbuch für Anorganische Chemie, 53 255
2. Harris, J.R. and Horne, R.W. 1991. Negative staining, in Harris J. R. (Ed.), Electron Microscopy in Biology, Oxford University Press, Oxford.
3. Adrian, M., Dubochet, J., Fuller, S.D. and Harris, J.R. 1998. Cryo-negative Staining. Micron 29, 145-160.
4. De Carlo, S., El-Bez, C., Alvarez-Rúa, C., Borge, J. and Dubochet, J. 2002. Cryo-negative staining reduces electron-beam sensitivity of vitrified biological particles. J. Struct. Biol. 138, 216-226.

[edit] External links

• Preparation of molybdate solutions
• MSDS safety data sheet

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