Chemical elements
    Physical Properties
    Chemical Properties
      Hypovanadous Oxide
      Vanadous Oxide
      Hypovanadic Oxide
      Vanadic Oxide
      Hypovanadous Fluoride
      Vanadous Fluoride
      Vanadium Tetrafluoride
      Vanadium Pentafluoride
      Vanadyl Difluoride
      Vanadium Oxytrifluoride
      Vanadium Dioxyfluoride
      Hypovanadous Chloride
      Vanadous Chloride
      Hypovanadic Chloride
      Divanadyl Chloride
      Vanadium Oxymonochloride
      Vanadyl Dichloride
      Vanadium Oxytrichloride
      Vanadium Oxydichloride
      Vanadous Bromide
      Hypovanadic Bromide
      Vanadium Oxymonobromide
      Vanadyl Dibromide
      Vanadium Oxytribromide
      Hydrated Vanadium Tri-iodide
      Vanadium Suboxide
      Hypovanadous Oxide
      Vanadous Oxide
      Hypovanadic Oxide
      Intermediate Vanadium Oxides
      Vanadium Pentoxide
      Sodium Stannovanadates
      Double Vanadates
      Heteropoly-Acids with Vanadium
      Pervanadic Acid
      Vanadium Monosulphide
      Vanadium Trisulphide
      Vanadium Pentasulphide
      Vanadium Oxysulphides
      Hypovanadous Sulphate
      Vanadous Sulphate
      Vanadyl Sulphites
      Vanadyl Sulphates
      Vanadic Sulphates
      Vanadyl Dithionate
      Ammonium Orthothiovanadate
      Ammonium Pyroxyhexathiovanadate
      Sodium Orthoxytrithiovanadate
      Sodium Orthoxymonothiovanadate
      Vanadium Selenides
      Vanadyl Selenite
      Vanadyl Selenates
      Vanadium Subnitride
      Vanadium Mononitride
      Vanadium Dinitride
      Alkali Vanadyl Nitrites
      Vanadium Nitrates
      Vanadyl Hypophosphite
      Vanadyl Phosphates
      Vanadous Pyrophosphate
      Vanadyl Arsenates
      Vanadium Carbide
      Vanadyl Cyanide
      Potassium Vanadocyanide
      Potassium Vanadicyanide
      Vanadium Ferrocyanides
      Ammonium Vanadyl Thiocyanate
      Vanadium Subsilicide
      Vanadium Disilicide
      Vanadium Boride
    Detection, Estimation
    PDB 1b8j-2i4e
    PDB 2jhr-6rsa

Pervanadic Acid, HVO4

Pervanadic Acid has not been definitely isolated in the solid state. When vanadium pentoxide is dissolved in hydrogen peroxide solution which also contains sulphuric acid, a red solution is formed from which on concentration in vacuo greyish-yellow crystals, which are assumed to have the composition HVO4, pervanadic acid, are deposited. They give the reactions of a per-acid, but are difficult to analyse in consequence of their unstable character. The preparation of the crystals is best carried out at low temperatures, because at ordinary temperatures vigorous evolution of oxygen takes place in consequence of the catalytic decomposition of the hydrogen peroxide by the vanadium pentoxide. A similarly coloured solution with similar properties is also obtained by the action of sulphuric acid on barium pervanadate. According to Meyer and Pawletta, the red solution contains the compound (VO2)2(SO4)3, which undergoes hydrolysis in the following manner:

(VO2)2(SO4)3 + 6H2O ⇔ 2VO2(OH)3 + 3H2SO4.
Reddish-brown ⇔ Yellow

The yellow compound VO2(OH)3 thus formed can be looked upon as a hydrated pervanadic acid, HVO4.H2O, or as peroxyorthovanadic acid, . It decomposes slowly at ordinary temperatures, and more rapidly on being warmed, with evolution of oxygen and reprecipitation of vanadium pentoxide.

It has been shown that in the formation of the red compound in solution each molecule of vanadium pentoxide reacts with two molecules of hydrogen peroxide:

V2O5 + 2H2O2 = 2HVO4 + H2O.

Pervanadic acid appears, therefore, to be formed from metavanadic acid, HVO3. This view of the reaction and the formula for pervanadic acid are further supported by titrating the red solution with caustic soda, when it is found that two molecules of caustic soda are required for each molecule of vanadium pentoxide. The monobasicity of the acid is confirmed by measuring the equivalent conductivities of solutions of potassium pervanadate.

A solution of pervanadic acid evolves a mixture of oxygen and chlorine on the addition of hydrochloric acid; it evolves oxygen slowly on standing, more rapidly on warming, and leaves a residue of vanadium pentoxide. Decomposition of the solution is accelerated by the presence of dilute sulphuric acid. Pervanadates of the alkali metals have been prepared by the action of hydrogen peroxide on the alkali metavanadates; pervanadates of several heavy metals have also been isolated by double decomposition with ammonium pervanadate. These salts vary from bright yellow to deep orange in colour, and are amorphous or micro-crystalline. They undergo hydrolysis in dilute solution, e.g.

KVO4 + H2OKVO3 + H2O2,

and evolve oxygen when platinised asbestos is introduced into their concentrated solutions. The following metapervanadates have been prepared: Ammonium pervanadate, NH4VO4; barium pervanadate, Ba(VO4)2; cadmium pervanadate, Cd(VO4)2; calcium pervanadate, Ca(VO4)2; lead pervanadate, Pb(VO4)2; lithium pervanadate, LiVO4; potassium pervanadate, KVO4; silver pervanadate, AgVO4; sodium pervanadate, NaVO4; and strontium pervanadate, Sr(VO4)2. Scheuer was unable to prepare the pervanadates of aluminium, cobalt, copper, magnesium, manganese, and nickel.

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