Sodium molybdate

Sodium molybdate
IUPAC name Sodium molybdate
Other names Disodium molybdate
Identifiers
CAS number	7631-95-0 Y,  10102-40-6 (dihydrate)
PubChem	4384450
EC number	231-551-7
RTECS number	QA5075000
Properties
Molecular formula	Na2MoO4
Molar mass	205.92 g/mol (anhydrous) 241.95 g/mol (dihydrate)
Appearance	White powder
Density	3.78 g/cm3, solid
Melting point	687 °C
Solubility in water	84 g/100 ml (100 °C)
Refractive index (nD)	1.714
Hazards
MSDS	External MSDS
EU Index	Not listed
NFPA 704	0 2 0
Flash point	Non-flammable
Related compounds
Other anions	Sodium chromate Sodium tungstate
Other cations	Ammonium molybdate
Y molybdate (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Sodium molybdate, Na₂MoO₄, is useful as a source of molybdenum.^[1] It is often found as the dihydrate, Na₂MoO₄·2H₂O.

The molybdate(VI) anion is tetrahedral. Two sodium cations coordinate with every one anion.^[2]

History

Sodium molybdate was first synthesized by the method of hydration.^[3] A more convenient synthesis is done by dissolving MoO₃ in sodium hydroxide at 50–70 °C and crystallizing the filtered product.^[2] The anhydrous salt is prepared by heating to 100 °C.

MoO₃ + 2NaOH → Na₂MoO₄·2H₂O

Uses

The agriculture industry uses 1 million pounds per year as a fertilizer. In particular, its use has been suggested for treatment of whiptail in broccoli and cauliflower in molybdenum-deficient soils.^[4][5] However, care must be taken because at a level of 0.3 ppm sodium molybdate can cause copper deficiencies in animals, particularly cattle.^[2]

It is used in industry for corrosion inhibition, as it is a non-oxidizing anodic inhibitor.^[2] The addition of sodium molybdate significantly reduces the nitrite requirement of fluids inhibited with nitrite-amine, and improves the corrosion protection of carboxylate salt fluids.^[6]

In industrial water treatment applications where galvanic corrosion is a potential due to bimetallic construction, the application of sodium molybdate is preferred over sodium nitrite. Sodium molybdate has the advantage in that the dosing of lower ppm's of molybdate allow for lower conductivity of the circulating water. Sodium molybdate at levels of 50-100 ppm offer the same levels of corrosion inhibition that sodium nitrite at levels of 800+ offer. By utilizing lower concentrations of sodium molybdate, conductivity is kept at a minimum and thus galvanic corrosion potentials are decreased.^[7]

Reactions

When reacted with sodium borohydride, molybdenum is reduced to a lower valent oxide:^[8]

Na₂MoO₄ + NaBH₄ + 2H₂O→ NaBO₂ + MoO₂ + 2NaOH+ 3 H₂

Sodium molybdate reacts with the acids of dithiophosphates:^[2]

Na₂MoO₄ + (RO)₂PS₂H (R = Me, Et) → [MoO₂(S₂P(OR)₂)₂]

which further reacts to form [MoO₃(S₂P(OR)₂)₄].

Safety

Sodium molybdate is incompatible with alkali metals, most common metals and oxidizing agents. It will explode on contact with molten magnesium. It will violently react with interhalogens (e.g., bromine pentafluoride; chlorine trifluoride). Its reaction with hot sodium, potassium or lithium is incandescent.^[9]

References

1. ^ Greenwood, Norman N.; Earnshaw, A. (1984). Chemistry of the Elements. Oxford: Pergamon. ISBN 0-08-022057-6. 
2. ^ ^{a b c d e} Braithwaite, E.R.; Haber, J. Molybdenum: An outline of its Chemistry and Uses. 1994. Elsevier Science B.V. Amsterdam, The Netherlands.
3. ^ Spitsyn, Vikt. I.; Kuleshov, I. M. Zhurnal Obshchei Khimii 1951. 21. 1701-15.
4. ^ Plant, W. (1950). "Use of Lime and Sodium Molybdate for the Control of ‘Whiptail’ in Broccoli". Nature 165 (4196): 533. doi:10.1038/165533b0. 
5. ^ Davies, E. B. (1945). "A Case of Molybdenum Deficiency in New Zealand". Nature 156 (3961): 392. doi:10.1038/156392b0. 
6. ^ Vukasovich, Mark S. Lubrication Engineering 1980. 36(12). 708-12.
7. ^ M. Houser, Corrosion Control Services, Inc., Introduction Handbook
8. ^ Chi Fo Tsang and Arumugam Manthiram. Journal of Materials Chemistry 1997. 7(6). 1003–1006.
9. ^ http://www.mallbaker.com/americas/msds/english/s4394_msds_us_default.pdf

External links

• Linus Pauling Institute page on molybdenum.