Sodium molybdate, Na₂MoO₄, is useful as a source of

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...

. This white, crystalline salt is often found as the dihydrate, Na₂MoO₄·2H₂O. The molybdate(VI) anion is tetrahedral. Two sodium cations coordinate with every one anion.Braithwaite, E.R.; Haber, J. ''Molybdenum: An outline of its Chemistry and Uses.'' 1994. Elsevier Science B.V. Amsterdam, The Netherlands.

History

Sodium molybdate was first synthesized by the method of hydration. A more convenient synthesis is done by dissolving MoO₃ in

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

at 50–70 °C and crystallizing the filtered product. 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 Broccoli (''Brassica oleracea'' var. ''italica'') is an edible green plant in the cabbage family (family Brassicaceae, genus ''Brassica'') whose large flowering head, stalk and small associated leaves are eaten as a vegetable. Broccoli is cl ...

and

cauliflower Cauliflower is one of several vegetables in the species ''Brassica oleracea'' in the genus ''Brassica'', which is in the Brassicaceae (or mustard) family. It is an annual plant that reproduces by seed. Typically, only the head is eaten – the ...

in molybdenum-deficient soils. However, care must be taken because at a level of 0.3 ppm sodium molybdate can cause copper deficiencies in animals, particularly cattle. It is used in industry for corrosion inhibition, as it is a non-oxidizing anodic inhibitor. 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. In industrial water treatment applications where

galvanic corrosion Galvanic corrosion (also called bimetallic corrosion or dissimilar metal corrosion) is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. A sim ...

is a potential due to bimetallic construction, the application of sodium molybdate is preferred over

sodium nitrite Sodium nitrite is an inorganic compound with the chemical formula NaNO2. It is a white to slightly yellowish crystalline powder that is very soluble in water and is hygroscopic. From an industrial perspective, it is the most important 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 as 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.

Reactions

When reacted with

sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds appli ...

, molybdenum is reduced to lower valent

molybdenum(IV) oxide Molybdenum dioxide is the chemical compound with the chemical formula, formula MoO. It is a violet-colored solid and is a metallic conductor. The mineralogical form of this compound is called tugarinovite, and is only very rarely found. Structur ...

: :Na₂MoO₄ + NaBH₄ + 2H₂O → NaBO₂ + MoO₂ + 2NaOH + 3H₂ Sodium molybdate reacts with the acids of dithiophosphates: :Na₂MoO₄ + → oO₂(S₂P(OR)₂)₂which further reacts to form oO₃(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

interhalogen In chemistry, an interhalogen compound is a molecule which contains two or more different halogen atoms ( fluorine, chlorine, bromine, iodine, or astatine) and no atoms of elements from any other group. Most interhalogen compounds known are b ...

s (e.g.,

bromine pentafluoride Bromine pentafluoride, Br F5, is an interhalogen compound and a fluoride of bromine. It is a strong fluorinating agent. BrF5 finds use in oxygen isotope analysis. Laser ablation of solid silicates in the presence of BrF5 releases O2 for subseq ...

;

chlorine trifluoride Chlorine trifluoride is an interhalogen compound with the formula ClF3. This colorless, poisonous, corrosive, and extremely reactive gas condenses to a pale-greenish yellow liquid, the form in which it is most often sold (pressurized at room temp ...

). Its reaction with hot sodium, potassium or lithium is incandescent.http://www.mallbaker.com/americas/msds/english/s4394_msds_us_default.pdf

References

External links

Linus Pauling Institute page on molybdenum
{{Molybdates Molybdates Sodium compounds Dietary minerals Inorganic compounds Corrosion inhibitors