Tungstic acid

Crystal structure
__ W 6+      __ O 2−      __ H +
General
Surname	Tungstic acid
other names	Tungsten (VI) oxide monohydrate Sheel acid
Ratio formula	WO 3 · H 2 O
Brief description	yellow, odorless solid
External identifiers / databases
CAS number 7783-03-1 EC number 231-975-2 ECHA InfoCard 100,029,068 PubChem 1152 Wikidata Q416538
properties
Molar mass	249.85 g mol −1
Physical state	firmly
density	5.5 g cm −3
Melting point	from 100 ° C (decomposition)
pK s value	3.5; 4.6
solubility	almost insoluble in water and acids soluble in alkalis
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Tungstic acid (more precisely, orthotungstic acid) is a compound of tungsten trioxide and water .

Extraction and presentation

Tungstic acid is formed, among other things, when tungstate solutions are acidified and the dihydrate (WO ₃ · 2 H ₂ O) which is initially precipitated is carefully heated .

For example, by reacting calcium tungstate with a mixture of concentrated hydrochloric acid and nitric acid .

${\displaystyle \mathrm {CaWO_{4}+2\ HX\longrightarrow H_{2}WO_{4}+CaX_{2}} }$

properties

The ratio formula of the tungsten trioxide monohydrate is H ₂ WO ₄ , but in contrast to the apparently analogous structure of sulfuric acid (H ₂ SO ₄ ), there are no discrete H ₂ WO ₄ molecules. Instead, tungstic acid consists of a layered lattice of WO ₆ octahedra. In contrast, the anions of tungstic acid, analogous to the sulfate ions , consist of WO ₄ ²⁻ tetrahedra. It was isolated for the first time by Carl Wilhelm Scheele in 1781 in Köping . Tungstic acid dissolves more easily in alkalis than tungsten trioxide .

Individual evidence

1. ^ KC von Leonhard : Scheelit. In: Handbuch der Oryktognosie , Verlag Mohr and Winter, Heidelberg 1821, pp. 594–596 ( PDF 233kB ; p. 2)
2. ↑ ^{a b c d} Entry on tungstic acid. In: Römpp Online . Georg Thieme Verlag, accessed on January 7, 2018.
3. ↑ ^{a b c d} Entry on tungstic acid in the GESTIS substance database of the IFA , accessed on December 19, 2019 (JavaScript required)
4. ^ ^{A b} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 .
5. ↑ Georg Brauer (ed.) U. a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume III, Ferdinand Enke, Stuttgart 1981, ISBN 3-432-87823-0 , p. 1566.