|Molar mass||293.82 g·mol−1|
|Appearance||white rhombohedral crystals|
|Density||4.179 g/cm3 (anhydrous)
3.25 g/cm3 (dihydrate)
|Melting point||698 °C (1,288 °F; 971 K)|
|57.5 g/100 mL (0 °C)
74.2 g/100 mL (25 °C)
96.9 g/100 mL (100 °C)
|Solubility||slightly soluble in ammonia
insoluble in alcohol, acid
|Crystal structure||rhombic (anhydrous)
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Sodium tungstate is the inorganic compound with the formula Na2WO4. This white, water-soluble solid is the sodium salt of tungstic acid. It is useful as a source of tungsten for chemical synthesis. It is an intermediate in the conversion of tungsten ores to the metal.
Preparation and structure
The predominant route to this salt is the extraction of tungsten ores, almost all of which are tungstates. Thus, the ores are treated with a base to give sodium tungstate, as illustrated in the case of wolframite:
- Fe/MnWO4 + 2 NaOH + 2 H2O → Na2WO4•2H2O + Fe/Mn(OH)2
Sodium tungstate can also be produced by treating tungsten carbide with a mixture of sodium nitrate and sodium hydroxide in a fusion process which overcomes the high exothermicity of the reaction involved.
Several polymorphs of sodium tungstate are known, three at only one atmosphere pressure. They feature tetrahedral orthotungstate dianions but differ in the packing motif. The WO42− anion adopts a structure like sulfate (SO42−).
Treatment of sodium tungstate with hydrochloric acid gives the trioxide:
- Na2WO4 + 2 HCl → WO3 + 2 NaCl + H2O
This reaction can be reversed using aqueous solution of sodium hydroxide
It is also known for its anti-diabetic effects; researchers have identified the pathways through which sodium tungstate improves pancreatic function and beta cell proliferation.
- Erik Lassner, Wolf-Dieter Schubert, Eberhard Lüderitz, Hans Uwe Wolf, "Tungsten, Tungsten Alloys, and Tungsten Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a27_229.
- Carl W. F. T. Pistorius "Phase Diagrams of Sodium Tungstate and Sodium Molybdate to 45 kbar" J. Chem. Phys. 1966, volume 44, 4532.doi:10.1063/1.1726669
- The Antidiabetic Agent Sodium Tungstate Activates Glycogen Synthesis through an Insulin Receptor-independent Pathway. The Journal of Biological Chemistry, Vol. 278, No. 44, Issue of October 31, pp. 42785–42794, 2003.
- The Anti-Diabetic Effects Of Sodium Tungstate Revealed, ScienceDaily, Aug. 28, 2009