Chemical elements
  Tungsten
    Isotopes
    Energy
    Production
    Preparation
    Application
    Physical Properties
    Chemical Properties
    Compounds
      Tungsten Hexafluoride
      Tungsten Oxyfluorides
      Tungsten Dichloride
      Double Chlorides of Trivalent Tungsten
      Tungsten Tetrachloride
      Tungsten Pentachloride
      Tungsten Hexachloride
      Tungsten Oxychlorides
      Tungsten Dibromide
      Tungsten Pentabromide
      Tungsten Hexabromide
      Tungsten Chlorobromides
      Tungsten Oxybromides
      Tungsten Di-iodide
      Tungsten Tetra-iodide
      Tungsten Dioxide
      Ditungsten Pentoxide
      Tungsten Trioxide
      Tungstic Acid
      Aluminium Tungstates
      Ammonium Tungstates
      Antimony Tungstates
      Barium Tungstates
      Normal Bismuth Tungstate
      Cadmium Tungstates
      Calcium Tungstates
      Cerium Tungstate
      Chromium Tungstates
      Cobalt Tungstates
      Copper Tungstates
      Indium Tungstate
      Iron Tungstates
      Lanthanum Tungstate
      Lead Tungstates
      Lithium Tungstates
      Magnesium Tungstates
      Manganese Tungstates
      Mercury Tungstates
      Neodymium Tungstate
      Nickel Tungstates
      Platinum Tungstates
      Potassium Tungstates
      Praseodymium Tungstate
      Rubidium Tungstates
      Samarium Tungstate
      Silver Tungstates
      Sodium Tungstates
      Strontium Tungstates
      Thallium Tungstates
      Tin Tungstates
      Uranium Tungstate
      Ytterbium Tungstates
      Yttrium Tungstate
      Zinc Tungstates
      Metatungstic Acid
      Ammonium Metatungstate
      Barium Metatungstate
      Cadmium Metatungstate
      Calcium Metatungstate
      Cerium Metatungstate
      Cobalt Metatungstate
      Lead Metatungstate
      Magnesium Metatungstate
      Mercurous Metatungstate
      Nickel Metatungstate
      Potassium Metatungstate
      Rubidium Metatungstate
      Samarium Metatungstate
      Silver Metatungstate
      Sodium Metatungstate
      Strontium Metatungstate
      Thallous Metatungstate
      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

Tungstocyanic Acid, H4[W(CN)8]






Tungstocyanic Acid, H4[W(CN)8].6H2O, may be prepared by treating the silver salt with a slight excess of cold dilute hydrochloric acid, and saturating the clear filtrate with hydrogen chloride below 0° C. The acid separates in yellow needles, and may be dried first in carbon dioxide and then in a desiccator over potassium hydroxide. It may also be obtained by the action of concentrated acid in the cold on the potassium salt. The product, which is soluble in water and in alcohol, is a strong acid and readily decomposes carbonates. The crystals deliquesce in moist air; if dried over sulphuric acid, they lose about three-fourths of their water content. When heated above 60° C. they decompose.

The salts of this acid are analogous to the corresponding molybdo-cyanides. Those of the alkali and alkaline earth metals are soluble in water, those of the heavier metals are insoluble, and all are insoluble in ordinary organic solvents. Many of the cyanides - for example, those of cadmium, copper, nickel, silver, and zinc - dissolve in concentrated ammonia solutions and yield, on recrystallisation, metal ammine derivatives. The tungstocyanides, which are generally yellow in colour, yield yellow neutral solutions which are generally stable and are unaffected by dilute acids or alkalies. Hot dilute nitric acid causes slight oxidation, whilst hot concentrated nitric or sulphuric acid causes complete decomposition. In dilute sulphuric acid solution the compounds of this series are oxidised by potassium permanganate in such a way that for each tungsten atom present one half atom of oxygen is used up. This fact appeared to contradict the presence of tetravalent tungsten, since in the usual course of oxidation, i.e. in passing from WIV to WVI, one atom of tungsten requires one atom of oxygen. However, investigation confirmed the tetravalency of tungsten, the product of oxidation being not tungstic acid, but a complex cyanide, containing pentavalent tungsten, of the type R3[W(CN)8]. The transformation of the anion may therefore be expressed

[WIV(CN)8]'''' → [WV(CN)8]'''

The valency of the tungsten in both these series of compounds is further confirmed by determining the amount of silver deposited on heating them for ten to twelve hours at 140° to 160° C. with ammoniacal silver nitrate in a sealed tube. The reaction takes place according to the equation

WVI-x + nAg = WVI + xAg + (n-x)Ag


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