Editing Tungsten trioxide (section)

==Preparation==
===Industrial===
Tungsten trioxide is obtained as an intermediate in the recovery of tungsten from its minerals.<ref name=prad2003/> Tungsten ores can be treated with [[alkali]]s to produce soluble [[tungstate]]s. Alternatively, CaWO<sub>4</sub>, or [[scheelite]], is allowed to react with [[HCl]] to produce [[tungstic acid]], which decomposes to WO<sub>3</sub> and water at high temperatures.<ref name=prad2003/>

:CaWO<sub>4</sub> + 2 HCl → CaCl<sub>2</sub> + H<sub>2</sub>WO<sub>4</sub>
:H<sub>2</sub>WO<sub>4</sub> → {{H2O}} + WO<sub>3</sub>

===Laboratory===
Another common way to synthesize WO<sub>3</sub> is by [[calcination]] of [[ammonium paratungstate]] (APT) under oxidizing conditions:<ref name=lass1999/>

:(NH<sub>4</sub>)<sub>10</sub>[H<sub>2</sub>W<sub>12</sub>O<sub>42</sub>]{{Hydrate|4}} → 12 WO<sub>3</sub> + 10 NH<sub>3</sub> + 10 {{H2O}}