Tungstic acid

Tungstic acid
Names
	IUPAC name dihydroxy-dioxotungsten
	Other names Orthotungstic acid
Identifiers
CAS Number	7783-03-1 ;
3D model (JSmol)	Interactive image;
ECHA InfoCard	100.029.068
EC Number	231-975-2;
PubChem CID	1152;
RTECS number	YO7840000;
UNII	J4D6K0RX2G ;
CompTox Dashboard (EPA)	DTXSID80894161 ;
	InChI InChI=1S/2H2O.2O.W/h2*1H2;;;/q;;;;+2/p-2 Key: CMPGARWFYBADJI-UHFFFAOYSA-L;
	SMILES O[W](=O)(=O)O;
Properties
Chemical formula	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)
Solubility in water	insoluble
Solubility	soluble in HF, ammonia ; slightly soluble in ethanol
Hazards
NFPA 704 (fire 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. Both a monohydrate (WO₃·H₂O) and hemihydrate (WO₃·0.5H₂O)[1] are known. Molecular species akin to sulfuric acid, i.e. (HO)₂WO₂ are not observed.

The solid-state structure of WO₃·H₂O consists of layers of octahedrally coordinated WO₅(H₂O) units where 4 vertices are shared.[2] The dihydrate has the same layer structure with the extra H₂O molecule intercalated.[2] 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.[3]

Tungstic acid

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.[4]

Uses

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

References

Günter, John R.; Amberg, Marcel; Schmalle, Helmut (1989). "Direct synthesis and single crystal structure determination of cubic pyrochlore-type tungsten trioxide hemihydrate, WO3 · 0.5H2O". Materials Research Bulletin. 24 (3): 289–292. doi:10.1016/0025-5408(89)90214-6.
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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[1] Günter, John R.; Amberg, Marcel; Schmalle, Helmut (1989). "Direct synthesis and single crystal structure determination of cubic pyrochlore-type tungsten trioxide hemihydrate, WO3 · 0.5H2O". Materials Research Bulletin. 24 (3): 289–292. doi:10.1016/0025-5408(89)90214-6.

[Wells-2] Wells, A.F. (1986). Structural inorganic chemistry (5th ed.). Oxford [Oxfordshire]: Clarendon Press. ISBN 0-19-855370-6.

[3] 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-4] Murau, P. C. (1961). "Dissolution of Tungsten by Hydrogen Peroxide". Analytical Chemistry. pp. 1125–1126. doi:10.1021/ac60176a021.