Chemical elements
  Molybdenum
    Isotopes
    Energy
    Production
    Application
    Physical Properties
    Chemical Properties
    Alloys
    Compounds
      Molybdenum Hexafluoride
      Fluoroxypermolybdates
      Molybdenum Dichloride
      Molybdenum Trichloride
      Molybdenum Tetrachloride
      Molybdenum Pentachloride
      Molybdenum Oxychlorides
      Chlormolybdic Acids
      Molybdenum Dibromide
      Molybdenum Tribromide
      Molybdenum Tetrabromide
      Molybdenum Oxybromide
      Molybdenum Di-iodide
      Molybdenum Oxyiodide
      Iodomolybdic Acid
      Molybdenum Sesquioxide
      Molybdenum Dioxide
      Molybdenum Oxide Blue
      Molybdenum Trioxide
      Molybdates
      Aluminium Molybdates
      Ammonium Molybdate
      Ammonium Dimolybdate
      Ammonium Paramolybdate
      Ammonium Trimolybdate
      Ammonium Tetramolybdate
      Ammonium Octamolybdate
      Barium Molybdates
      Barium Paramolybdate
      Barium Trimolybdate
      Barium Tetramolybdate
      Barium Octamolybdate
      Barium Nonamolybdate
      Beryllium Molybdate
      Bismuth Molybdates
      Cadmium Molybdates
      Caesium Molybdates
      Calcium Molybdate
      Calcium Trimolybdate
      Calcium Tetramolybdate
      Calcium Octamolybdate
      Chromium Molybdates
      Cobalt Molybdates
      Cobalt Dimolybdate
      Cobalt Trimolybdate
      Copper Molybdates
      Ferrous Molybdate
      Ferric Molybdate
      Indium Molybdate
      Lead Molybdates
      Lithium Molybdate
      Lithium Dimolybdate
      Lithium Paramolybdate
      Lithium Trimolybdate
      Lithium Tetramolybdate
      Magnesium Molybdates
      Magnesium Paramolybdate
      Magnesium Trimolybdate
      Manganese Molybdate
      Mercurous Molybdates
      Nickel Molybdates
      Potassium Molybdate
      Potassium Dimolybdate
      Potassium Paramolybdate
      Potassium Trimolybdate
      Potassium Tetramolybdate
      Potassium Octamolybdate
      Potassium Decamolybdate
      Rhodium Molybdates
      Rubidium Molybdate
      Rubidium Dimolybdate
      Rubidium Paramolybdate
      Rubidium Trimolybdate
      Rubidium Tetramolybdates
      Silver Molybdates
      Normal Silver Molybdate
      Sodium Molybdate
      Sodium Dimolybdate
      Sodium Paramolybdate
      Sodium Trimolybdate
      Sodium Tetramolybdate
      Sodium Iodomolybdate
      Strontium Molybdate
      Thallous Molybdate
      Thallous Paramolybdate
      Thallous Tetramolybdate
      Thorium Molybdate
      Uranium Molybdates
      Uranyl Octamolybdate
      Zinc Molybdates
      Zinc Trimolybdate
      Zinc Tetramolybdate
      Zinc Octamolybdate
      Zirconium Molybdate
      Permolybdic Acid
      Molybdenum Sesquisulphide
      Molybdenum Disulphide
      Dimolybdenum Pentasulphide
      Molybdenum Trisulphide
      Molybdenum Tetrasulphide
      Thiomolybdates
      Ammonium Thiomolybdates
      Ammonium Molybdosulphites
      Potassium Thiomolybdate
      Potassium Thiodimolybdate
      Potassium Dithiodioxymolybdate
      Potassium Molybdosulphite
      Sodium Thiomolybdates
      Sodium Molybdosulphites
      Molybdenum Sulphates
      Molybdenum Selenide
      Complex Molybdoselenites
      Chromates of Molybdenum
      Molybdenum Phosphide
      Molybdic Metaphosphate
      Heteropoly-compounds with Phosphorus
      12-Molybdophosphoric Acid
      9-Molybdophosphoric Acid
      172-Molybdophosphoric Acid
      Molybdohypophosphates
      Molybdophosphites
      Molybdohypophosphites
      12-Molybdo-arsenates
      9-Molybdo-arsenates
      3-Molybdo-arsenates
      Molybdenum Carbides
      Molybdenum Carbonyl
      Reddish-violet Salts
      Yellow Salts
      Thiocyanates of Molybdenum
      Molybdenum Monosilicide
      Molybdenum Sesquisilicide
      Molybdenum Disilicide
      Molybdosilicic Acid and Molybdosilicates
      12-Molybdosilicic Acid
    PDB 1aa6-1qh8
    PDB 1r27-2jir
    PDB 2min-3unc
    PDB 3uni-4f6t

Molybdates






Normal molybdates of the type R2MoO4 exist in solution but are relatively unstable, and readily form acid salts or complex poly molybdates. Thus dimolybdates, R2Mo2O7, can be obtained by fusion of molybdenum trioxide with sodium or potassium nitrate; trimolvbdates, R2Mo3O10, and tetramolybdates, R2Mo4O13, by heating molybdenum trioxide with an aqueous solution of sodium or potassium carbonate. Even more highly acid salts - for example, octa- and deca-molybdates - can be obtained. Solutions of normal molybdates, when treated with hydrochloric acid or nitric acid, yield a precipitate of acid molybdate; this reaction does not, however, take place with sulphuric, acetic, oxalic, or tartaric acids.

Different views have been expressed concerning the relation between the various types of poly molybdates. According to Rosenheim and his collaborators, the tetramolybdates are entirely similar to the meta-tungstates, and are therefore 12-molybdic acid hydrates of the type

R6H4[H2(Mo2O7)6],
whilst the octamolybdates, which yield hydrogen ions in aqueous solutions, are regarded as hydrogen salts with the same complex anion,
R3H7[H2(Mo2O7)6].

The same authors state that two distinct series of decamolybdates exist, either isomeric or polymeric, one sparingly soluble, and the other readily soluble, in water. The paramolybdates, which have been described under various formulae, appear to correspond with either 3R2O.7MoO3.aq. or 5R2O.12MoO3.aq. It has been suggested that these salts are derived from the hypothetical orthomolybdic acid H6MoO6 by partial substitution of the group Mo2O7 for oxygen, and may be formulated
R6[Mo(Mo2O7)3O3].
Condensation formulae have also been suggested. For example, ammonium paramolybdate, which has been obtained in the crystalline form in the anhydrous state, may be expressed by the formula

(NH4O)3MoO(O.MoO2)5O.MoO(ONH4)3,

and this view is supported by the preparation of two other ammonium heptamolybdates, of composition

(NH4O)3MoO(O.MoO2)5O.MoO2.OH
and
NH4O.(OH)2MoO(O.MoO2)5O.MoO2.OH.H2O.

When increasing quantities of hydrochloric acid are added to a saturated solution of ammonium paramolybdate, a series of hexabasic polymolybdates, having the general formula

(NH4O)3MoO(O.MoO2)mO.MoO(ONH4)3 + nH2O,

are obtained. Of these, compounds containing 9, 11, 12, and 13 atoms of molybdenum to the molecule have been prepared. All these poly-molybdates, with excess of alkali, yield orthomolybdates, which may be regarded as hexabasic trimolybdates,

(RO)3MoO.O.MoO2.O.MoO(OR)3 + nH2O.

A series of tetrabasic polymolybdates, containing up to seven molybdic groups, arise by the decomposition of the tridecamolybdates, and compounds containing more than thirteen molybdic groups are not known. The condensation of molybdic acid thus reaches its limit by the formation of tridecamolybdic acid.

The classification of molybdates into ortho-, meta-, and para-salts is obviously unsatisfactory. There appear to be two main groups of molybdates: (1) the hexabasic poly molybdates, which include among others the ortho- and para-molybdates; and (2) the tetrabasic poly-molybdates, including the metamolybdates, which arise from the hexabasic salts by hydrolytic rupture of their chain.

Molybdates combine also with other acidic oxides, forming a series of complex molybdates, the most important of which are probably the phosphomolybdates. The formation of such compounds as dichlormolybdic acid or molybdenum hydroxychloride, MoOCl2(OH)2, and the sulphate MoO3.SO3, illustrate the behaviour of molybdenum trioxide as a basic oxide.

The absorption spectra of molybdates have been investigated.

Molybdates in aqueous solution are reduced by the common reducing agents, yielding solutions which are reddish, blue, green, or brown, according to the prevailing conditions. Hydrogen sulphide, for instance, produces at first a yellowish colour, changing to green and then blue; finally a brown precipitate of molybdenum sulphide is obtained. For further discussion upon the reactions of molybdates.


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