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

Sodium molybdate

It is often found as the dihydrate, Na2MoO4•2H2O.
The molybdate(VI) anion is tetrahedral. Two sodium cations coordinate with every one anion.
History
Sodium molybdate was first synthesized by the method of hydration. A more convenient synthesis is done by dissolving MoO3 in sodium hydroxide at 50–70 °C and crystallizing the filtered product. 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. 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.
Reactions
When reacted with sodium borohydride, molybdenum is reduced to a lower valent oxide:
Na2MoO4 + NaBH4 + 2H2O→ NaBO2 + MoO2 + 2NaOH+ 3 H2
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].
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.

钼酸钠

概况
分子式：Na2MoO4•2H2O
分子量：241.95
CAS号：7631-95-0
性质：　白色菱形结晶。微溶于1.7份冷水，0.9份热水,25℃时5％的水溶液pH值9.0～10.0，不溶于丙酮。加热至100℃失去结晶水变成无水物。
标准：Na2MoO4•2H20≥99％（一级品）；98％（二级品）
制法：　钼精矿（主要组分为MoS2）经氧化焙烧生成三氧化钼，再用碱液浸取，得钼酸钠溶液，浸出液经抽滤、蒸发浓缩。浓缩液经冷却结晶、离心分离、干燥，即得钼酸钠。
用途：　钼酸盐毒性较低，对环境污染污染程度低，是目前应用较多的一种新型水处理剂。为了获得较好的缓蚀效果，钼酸盐常与聚磷酸盐、葡萄糖酸盐、锌盐、苯并三氮唑复配使用，这样不仅可以减少钼酸盐的使用量，而且可以提高缓蚀效果，复配后钼酸盐的用量由200～500mg／L下降至4～6mg／L。钼酸盐成膜过程中，必须要有溶解氧存在，而无需钙离子（或其他二价金属离子）。钼酸盐热稳定性高，可用于热流密度高及局部过热的循环水系统。
安全性：　钼酸钠有毒，但属低毒化合物。钼中毒会引起关节疼痛，造成血压偏低和血压波动，神经功能紊乱，代谢过程出现障碍。可溶性钼化物气溶胶最高容许浓度为2mg／m，粉尘为4mg／m。接触和使用钼酸钠时，要穿戴规定的防护用具。注意防潮。运输时须防雨淋、日晒。
用途：用于制造生物碱、油墨、化肥、钼红颜料和耐晒颜料的沉淀剂、催化剂、钼盐，也可用于制造阻燃剂和无公害型冷水系统的金属抑制剂，还用作镀锌、磨光剂及化学试剂。