Sodium tungstate

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Sodium tungstate
Sodium tungstate
Names
IUPAC name
Sodium tungstate
Identifiers
3D model (JSmol)
ECHA InfoCard 100.033.389
RTECS number
  • YO7875000
Properties
Na2WO4
Molar mass 293.82 g/mol
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
Structure
Rhombic (anhydrous)
orthorhombic (dihydrate)
Hazards
Safety data sheet External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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.[1]

Preparation and structure[edit]

Sodium tungstate is obtained by digestion of tungsten ores, the economically important representatives of which are tungstates, in base. Illustrative is the extraction of sodium tunstate from wolframite:[1]

Fe/MnWO4 + 2 NaOH + 2 H2O → Na2WO4•2H2O + Fe/Mn(OH)2

Scheelite is treated similarly using sodium carbonate.

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−).[2]

Reactions[edit]

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

Uses[edit]

The dominant use of sodium tungstate is as an intermediate in the extraction of tungsten from its ores, almost all of which are tungstates.[1] Otherwise sodium tungstate has only niche applications.

In organic chemistry, sodium tungstate is used as catalyst for epoxidation of alkenes and oxidation of alcohols into aldehydes or ketones. It exhibits anti-diabetic effects.[3]

Solutions of sodium polytungstate are used in density separation, since such mixtures are less toxic than bromoform and methylene iodide, but still have densities that fall between a number of naturally coupled minerals.[4]

References[edit]

  1. ^ a b c Lassner, Erik; Schubert, Wolf-Dieter; Lüderitz, Eberhard; Wolf,, Hans Uwe (2005). "Tungsten, Tungsten Alloys, and Tungsten Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a27_229.CS1 maint: extra punctuation (link)
  2. ^ 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
  3. ^ 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.
  4. ^ Improved density gradient separation techniques using Sodium Polytungstate and a comparison to the use of other heavy liquids. Report, U.S. Geological Survey, 1993.

External links[edit]