Sodium molybdate

Sodium molybdate, Na2MoO4, is useful as a source of molybdenum.

It is often found as the dihydrate, Na2MoO4. 2H2O.

The structure of the Molybdate (IV) anion is tetrahedral. Two sodium cations coordinate with every one anion.[2]



History
Sodium Molybdate was first synthesized by the method of hydration[1]; however, a more convenient synthesis is done by dissolving MoO3 in sodium hydroxide at 50-70 ºC and crystallizing the filtered product.[2] The anhydrous salt is prepared by heating to 100 ºC.

MoO3 + 2NaOH → Na2MoO4 ∙ 2H2O

Uses
Sodium molybdate is used in biochemistry and medicinal chemistry to track various organic chemicals that are colorless after a chromatographical procedure, which it always stains it blue. The blue color is also called molybdenum blue.

The agriculture industry uses 1 million pounds per year as a fertilizer. 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 for water treatment.

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.[3]

According to an article from 1950 that was published in Nature, sodium molybdate is useful for curing a broccoli disease known as ‘whiptail’.

Reactions
When reacted with sodium borohydride, molybdenum is reduced to a lower valent oxide:

Na2MoO4 + NaBH4 + 2H2O→ NaBO2 + MoO2+2NaOH+ 3 H2 [4]

Sodium molybdate reacts with the acids of dithiophosphates:

Na2MoO4 + (RO)2PS2H (R = Me, Et) → [MoO2(S2P(OR)2)2] which further reacts to form [MoO3(S2P(OR)2)4].[2]

Precautions
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. (From the MSDS)