Tungstic acid refers to hydrated forms of tungsten trioxide, WO<sub>3</sub>. Both a monohydrate (WO<sub>3</sub>÷H<sub>2</sub>O) and hemihydrate (WO<sub>3</sub>÷<sup>1</sup>/<sub>2</sub> H<sub>2</sub>O) are known. Molecular species akin to sulfuric acid, i.e. (HO)<sub>2</sub>WO<sub>2</sub> are not observed.
The solid-state structure of WO<sub>3</sub>÷H<sub>2</sub>O consists of layers of octahedrally coordinated WO<sub>5</sub>(H<sub>2</sub>O) units where 4 vertices are shared. The dihydrate has the same layer structure with the extra H<sub>2</sub>O molecule intercalated. 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.
Tungstic acid is obtained by the action of strong acids on solutions of alkali metallic tungstates. It can also be obtained from pure tungsten by reaction with hydrogen peroxide. Most tungsten(VI) compounds hydrolyze into tungstic acid or a mix of tungstates, except for stable polyoxometallates such as phosphotungstic acid.
It is used as a mordant and a dye in textiles.