Tungstic acid

Tungstic acid
Names
IUPAC name
dihydroxy-dioxotungsten
Other names
Orthotungstic acid
Identifiers
3D model (JSmol)
ECHA InfoCard 100.029.068
EC Number 231-975-2
RTECS number YO7840000
UNII
Properties
H2WO4
Molar mass 249.853 g/mol
Appearance yellow powder
Density 5.59 g/cm3
Melting point 100 °C (212 °F; 373 K) (decomposes)
Boiling point 1,473 °C (2,683 °F; 1,746 K)
insoluble
Solubility soluble in HF, ammonia
slightly soluble in ethanol
Hazards
NFPA 704
Flammability code 0: Will not burn. E.g., waterHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
2
0
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

Tungstic acid refers to hydrated forms of tungsten trioxide, WO3. The simplest form, the monohydrate, is WO3·H2O, H2WO4. The dihydrate WO3·2H2O is also known. The solid-state structure of WO3·H2O consists of layers of octahedrally coordinated WO5(H2O) units where 4 vertices are shared.[1] The dihydrate has the same layer structure with the extra H2O molecule intercalated between the layers.[1] The monohydrate is a yellow solid and insoluble in water. The classical name for this acid is 'acid of wolfram'. Salts of tungstic acid are tungstates.

The acid was discovered by Carl Wilhelm Scheele in 1781.[2]

Preparation

Tungstic acid is obtained by the action of strong acids on solutions of alkali metallic tungstates. It may also be prepared from the reaction between hydrogen carbonate and sodium tungstate. It can also be obtained from pure tungsten by reaction with hydrogen peroxide.[3]

Uses

It is used as a mordant and a dye in textiles.

References

  1. 1 2 Wells, A.F. (1986). Structural inorganic chemistry (5th ed.). Oxford [Oxfordshire]: Clarendon Press. ISBN 0-19-855370-6.
  2. ↑ Scheele, Carl Wilhelm (1781) "Tungstens bestånds-delar" (Tungsten's [i.e., Scheelite's] constituents), Kungliga Vetenskaps Academiens Nya Handlingar (Royal Scientific Academy's New Proceedings), 2: 89–95. (in Swedish)
  3. ↑ Murau, P. C. (1961). "Dissolution of Tungsten by Hydrogen Peroxide". Analytical Chemistry. pp. 1125–1126. doi:10.1021/ac60176a021.
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