Sodium molybdate

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

Sodium molybdate
Names
IUPAC name
Sodium molybdate
Other names
Disodium molybdate
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.028.683
EC Number
  • 231-551-7
RTECS number
  • QA5075000
UNII
Properties
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 (1,269 °F; 960 K)
84 g/100 ml (100 °C)
1.714
Hazards
Safety data sheet External MSDS
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
2
0
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
4000 mg/kg (rat, oral)[1]
>2080 mg/m3 (rat, 4 hr)[1]
Related compounds
Other anions
 Sodium chromate
Sodium tungstate
Other cations
 Ammonium molybdate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

The molybdate(VI) anion is tetrahedral. Two sodium cations coordinate with every one anion.[3]

History

Sodium molybdate was first synthesized by the method of hydration.[4] A more convenient synthesis is done by dissolving MoO3 in sodium hydroxide at 50–70 °C and crystallizing the filtered product.[3] The anhydrous salt is prepared by heating to 100 °C.

MoO3 + 2NaOH + H2O → 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.[5][6] However, care must be taken because at a level of 0.3 ppm sodium molybdate can cause copper deficiencies in animals, particularly cattle.[3]

It is used in industry for corrosion inhibition, as it is a non-oxidizing anodic inhibitor.[3] 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.[7]

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+ ppm. By utilizing lower concentrations of sodium molybdate, conductivity is kept at a minimum and thus galvanic corrosion potentials are decreased.[8]

Reactions

When reacted with sodium borohydride, molybdenum is reduced to lower valent molybdenum(IV) oxide:[9]

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

Sodium molybdate reacts with the acids of dithiophosphates:[3]

Na2MoO4 + (R = Me, Et)(RO)2PS2H → [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.[10]

References
  1. "Molybdenum (soluble compounds, as Mo)". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  2. Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. ISBN 978-0-08-022057-4.
  3. Braithwaite, E.R.; Haber, J. Molybdenum: An outline of its Chemistry and Uses. 1994. Elsevier Science B.V. Amsterdam, The Netherlands.
  4. Spitsyn, Vikt. I.; Kuleshov, I. M. Zhurnal Obshchei Khimii 1951. 21. 1701-15.
  5. Plant, W. (1950). "Use of Lime and Sodium Molybdate for the Control of 'Whiptail' in Broccoli". Nature. 165 (4196): 533. Bibcode:1950Natur.165..533P. doi:10.1038/165533b0.
  6. Davies, E. B. (1945). "A Case of Molybdenum Deficiency in New Zealand". Nature. 156 (3961): 392. Bibcode:1945Natur.156..392D. doi:10.1038/156392b0.
  7. Vukasovich, Mark S. Lubrication Engineering 1980. 36(12). 708-12.
  8. M. Houser, Corrosion Control Services, Inc., Introduction Handbook
  9. Tsang, Chi Fo; Manthiram, Arumugam (1997). "Synthesis of lower-valent molybdenum oxides in aqueous solutions by reducing Na2MoO4 with NaBH4". Journal of Materials Chemistry. 7 (6): 1003–1006. doi:10.1039/A606389F. ISSN 1364-5501.
  10. http://www.mallbaker.com/americas/msds/english/s4394_msds_us_default.pdf%5B%5D
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