Chemical elements
  Tungsten
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      Tungsten Hexafluoride
      Tungsten Oxyfluorides
      Tungsten Dichloride
      Double Chlorides of Trivalent Tungsten
      Tungsten Tetrachloride
      Tungsten Pentachloride
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      Ditungsten Pentoxide
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      Tungstic Acid
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      Barium Tungstates
      Normal Bismuth Tungstate
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      Metatungstic Acid
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      Calcium Metatungstate
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      Mercurous Metatungstate
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      Sodium Metatungstate
      Strontium Metatungstate
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      Zinc Metatungstate
      Pertungstic Acid
      Tungsten Bronzes
      Potassium Tungsten Bronze
      Lithium Tungsten Bronze
      Lithium Potassium Tungsten Bronze
      Sodium tungsten bronzes
      Tungsten Disulphide
      Tungsten Trisulphide
      Thiotungstates
      Tungsten Diselenide
      Tungsten Triselenide
      Tungsten Phosphides
      Tungsten Diphosphide
      Tritungsten Tetraphosphide
      Tungsten Monophosphide
      Tungsten Subphosphide
      Phosphotungstic Acids
      12-Tungstophosphoric Acid
      11-Tungstophosphates
      21:2-Tungstophosphoric Acid
      10-Tungstophosphoric Acid
      9-Tungstophosphoric Acid
      17:2-Tungstophosphates
      3-Tungstophosphates
      Hypophosphotungstates
      Tungsten Diarsenide
      Tungsten Chloro-arsenide
      12-Tungsto-arsenates
      11-Tungsto-arsenates
      9-Tungsto-arsenic Acid
      17:2-Tungsto-arsenates
      Tungsto-arsenites
      Tritungsten Carbide
      Ditungsten Carbide
      Tungsten Monocarbide
      Tungsten Iron Carbides
      Tungstocyanic Acid
      Ammonium Tungstocyanide
      Calcium Tungstocyanide
      Cadmium Tungstocyanide
      Caesium Tungstocyanide
      Lead Tungstocyanide
      Magnesium Tungstocyanide
      Manganese Tungstocyanide
      Potassium Tungstocyanide
      Rubidium Tungstocyanide
      Silver Tungstocyanide
      Sodium Tungstocyanide
      Strontium Tungstocyanide
      Thallium Tungstocyanide
      Zinc Tungstocyanide
      Tungsticyanic Acid
      Tungsten Sesquisilicide
      Tungsten Disilicide
      Tungsten Trisilicide
      12-Tungstosilicic Acid
      Iso-12-tungstosilicic Acid
      10-Tungstosilicates
      Tungsten Boride
      12-Tungstoboric Acid
      Iso-12-tungstoboric Acid
    Alloys
    PDB 1aor-2rav
    PDB 2rb5-6fit

9-Tungstophosphoric Acid






9-Tungstophosphoric Acid, (P2O5:WO3 = 1:18), luteophospho- tungstic acid, is formed by treating the 12- or 11-tungstophosphoric acid solutions with excess of phosphoric acid. It may best be prepared from its salts, for example, by treating the ammonium salt with aqua regia, or by decomposing the silver salt with hydrochloric acid. A colourless solution is obtained, which on evaporation turns yellow, and lemon-yellow hexagonal crystals separate. These melt at 28° C. and are very soluble in water. The acid probably exists in two isomeric forms. Its composition is represented by the formula P2O5.18WO3.42H2O, and its basicity appears to be 10 (see below), so that the constitutional formula

H5[P(OH)(W2O7)4-W2O7-(W2O7)4(OH)P]H5.36H2O

has been suggested. In this case an inner bridge connects the two nuclei. This is supported by conductivity measurements and a study of the neutralisation curves. The corresponding molybdo-phosphoric acid is 12-basic, but the complex ion in that acid is not so stable as the tungstic ion. The hydrogen-ion concentration in a 0.005 N solution of 9-tungstophosphoric acid is 4.1×10-3.

Salts of this acid may be prepared by boiling a mixture containing normal sodium tungstate, Na2WO4.2H2O (2 parts), syrupy phosphoric acid (3 parts), and water (1 part). The solution turns yellow, and on evaporation and cooling, greenish-yellow plates consisting of a mixture of sodium salts separate. If, instead of permitting crystallisation, the mixture is oxidised with a few drops of concentrated nitric acid, allowed to cool, and solid potassium or ammonium chloride added, yellow triclinic prisms of the potassium or ammonium salt separate. These may be purified by repeated crystallisation. They are readily soluble in water, and have composition

3K2O.P2O5.18WO3.14H2O,
3(NH4)2O.P2O5.18WO3.14H2O.

These salts, as well as the corresponding sodium and barium salts, may also be obtained by treating the free acid with the corresponding carbonate or chloride. The silver salt, 3Ag2O.P2O5.18WO3.16H2O, is prepared by treating a solution of the potassium salt with silver nitrate.

These acid salts correspond to the acid salts of 9-molybdo-phosphoric acid. The following salts, which show a basicity of 10, and appear to be the normal salts of the acid, have also been prepared:

5Ag2O.P2O5.18WO3.34H2O,
5(CN3H6)2O.P2O5.18WO3.18H2O.

The silver salt is obtained by treating a 30 per cent, solution of the acid with 5 to 6 molecular proportions of sodium hydroxide, and adding a soluble silver salt. A yellow flaky precipitate results which is almost insoluble in water. The guanidine salt is produced similarly, and yields bright yellow aggregates of small tables which are only slightlv soluble in water.


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