Vanadium(V) oxide

Vanadium(V) oxide ("vanadia") is the inorganic compound with the formula V2O5. Commonly known as vanadium pentoxide, it is a brown/yellow solid, although when freshly precipitated from aqueous solution, its colour is deep orange. Because of its high oxidation state, it is both an amphoteric oxide and an oxidizing agent. From the industrial perspective, it is the most important compound of vanadium, being the principal precursor to alloys of vanadium and is a widely used industrial catalyst.
The mineral form of this compound, shcherbinaite, is extremely rare, almost always found among fumaroles. A mineral trihydrate, V2O5·3H2O, is also known under the name of navajoite.
Chemical properties.
Reduction to lower oxides.
Upon heating a mixture of vanadium(V) oxide and vanadium(III) oxide, comproportionation occurs to give vanadium(IV) oxide, as a deep-blue solid:
The reduction can also be effected by oxalic acid, carbon monoxide, and sulfur dioxide. Further reduction using hydrogen or excess CO can lead to complex mixtures of oxides such as V4O7 and V5O9 before black V2O3 is reached.
Acid-base reactions.
V2O5 is an amphoteric oxide. Unlike most metal oxides, it dissolves slightly in water to give a pale yellow, acidic solution. Thus V2O5 reacts with strong non-reducing acids to form solutions containing the pale yellow salts containing dioxovanadium(V) centers:
It also reacts with strong alkali to form polyoxovanadates, which have a complex structure that depends on pH. If excess aqueous sodium hydroxide is used, the product is a colourless salt, sodium orthovanadate, Na3VO4. If acid is slowly added to a solution of Na3VO4, the colour gradually deepens through orange to red before brown hydrated V2O5 precipitates around pH 2. These solutions contain mainly the ions HVO42− and V2O74− between pH 9 and pH 13, but below pH 9 more exotic species such as V4O124− and HV10O285− (decavanadate) predominate.
Upon treatment with thionyl chloride, it converts to the volatile liquid vanadium oxychloride, VOCl3:
Other redox reactions.
Hydrochloric acid and hydrobromic acid are oxidised to the corresponding halogen, e.g.,
Vanadates or vanadyl compounds in acid solution are reduced by zinc amalgam through the colourful pathway:
[[File:Vanadium oxidation states.jpg|none|300px|thumb|
[[Category:Vanadium compounds]]
[[Category:Catalysts]]
[[Category:Infrared sensor materials]]
[[Category:IARC Group 2B carcinogens]]
[[Category:Oxidizing agents]]
[[Category:Transition metal oxides]]