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. The dihydrate has the same layer structure with the extra H2O molecule intercalated between the layers. 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.
3D model (JSmol)
|Molar mass||249.853 g/mol|
|Melting point||100 °C (212 °F; 373 K) (decomposes)|
|Boiling point||1,473 °C (2,683 °F; 1,746 K)|
|Solubility||soluble in HF, ammonia |
slightly soluble in ethanol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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.
- Wells, A.F. (1986). Structural inorganic chemistry (5th ed.). Oxford [Oxfordshire]: Clarendon Press. ISBN 0-19-855370-6.
- 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)
- Murau, P. C. (1961). "Dissolution of Tungsten by Hydrogen Peroxide". Analytical Chemistry. pp. 1125–1126. doi:10.1021/ac60176a021.
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