Chemical elements
  Tungsten
    Isotopes
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    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

Potassium Tungstates






The anhydrous normal salt, K2WO4, is prepared by fusing together equivalent quantities of tungstic anhydride and potassium hydroxide or potassium carbonate, the resulting mass being taken up with water and allowed to crystallise; or by boiling a solution of potassium hydroxide or carbonate in presence of tungstic acid. Thin, needle-shaped, monoclinic prisms, with axial ratio,

a:b:c = 1.9702:1:1.2341; and β = 113° 15',

and isomorphous with potassium manganate and potassium molybdate,1 are obtained, which are readily soluble in water, decrepitate when heated, and melt at about 921° to 926° C. The salt, however, appears to be dimorphous, laminated crystals often accompanying the prisms.

The dihydrate, K2WO4.2H2O, crystallises when the solution is concentrated over sulphuric acid at temperatures below 10° C. in lustrous monoclinic prisms and tables, with axial ratio

a:b:c = 0.9998:1:0.7880; and β = 110° 57'.

The crystals effloresce in dry air, but are deliquescent in moist air. Other hydrates have been described, for example, K2WO4.H2O, slender needles, which was probably partly dehydrated dihydrate; and K2WO4.5H2O, hexagonal prisms, which according to Ullik was a sodium-potassium tungstate.

The solution of normal potassium tungstate is strongly alkaline in reaction; its density at various concentrations at 15° C. has been determined as follows:

Concentration (per cent.)2.426.578.7216.19
Density1.02021.05751.07811.1548


Various acid tungstates have been described. The compound formulated as the ditungstate, K2O.2WO3.3H2O, in earlier literature has been shown to be the paratungstate.

Potassium paratungstate, 5K2O.12WO3.11H2O or 3K2O.7WO3.6H2O, is prepared by the action of acid on the normal tungstate; for example, (i) by saturating a solution with carbon dioxide, (ii) by adding acetic acid to a cold concentrated solution and boiling the resulting white precipitate with water, or (iii) by boiling the solution with a solution of tungstic acid. It may also be obtained by fusing together tungstic anhydride with potassium carbonate or potassium tungstate, and lixiviating the fused mass. The salt is deposited from solution as a crystalline powder consisting of iridescent scales. Electrolysis of a solution of the normal tungstate in a cell in which the electrodes are separated by a diaphragm also yields the paratungstate.

The crystals are triclinic pinacoids,

a:b:c = 0.9137:1:1.1362; α = 65° 36', β = 117° 22', γ = 115° 39',

and are isomorphous with ammonium paratungstate. The salt is somewhat soluble in cold water and dissolves readily in hot. Solubility data by Anthon, Riche, and Marignac are not in agreement. According to the last named, 1 part of the salt dissolves in 71 parts of water at 20° C., but when a saturated solution is prepared by boiling the salt with water for several days the cooled solution at 18° C. contains 1 part of the salt

after 1 day dissolved in 5.62 parts of water
after 26 day dissolved in 11.9 parts of water
after 153 day dissolved in 15.6 parts of water
after 334 day dissolved in 15.6 parts of water

It is insoluble in alcohol. When heated it loses water, and at a red heat fuses, undergoing decomposition,2 and on cooling sets to a yellow crystalline mass.

Two other hydrates of potassium paratungstate, 5K2O.12WO3.10H2O and 5K2O.12WO3.14H2O, or 3K2O.7WO3.8H2O, have been described.

The salt, 2K2O.5WO3.4H2O, is obtained as an amorphous precipitate by adding a cold concentrated solution of the normal salt to excess of glacial acetic acid; it is soluble in 20 parts of water, and the solution on evaporation at ordinary temperatures deposits prismatic tables. The solution decomposes on boiling. This salt may also be produced by the addition of potassium chloride to a hot solution of sodium paratungstate, or by crystallisation from a hot solution of potassium paratungstate.

Potassium tritungstate, K2O.3WO3.2H2O, is obtained, by pouring a concentrated solution of the normal salt into a boiling solution of acetic acid, as a white precipitate, which must be filtered immediately and washed with alcohol in order to prevent the formation of metatungstate. It dissolves in 5 to 6 parts of water, and the solution on concentration yields fine needle-shaped crystals or prisms; but on boiling or prolonged heating decomposition occurs.

The acid salts, 5K2O.14WO3 and K2O.8WO3, have also been described.

The double tungstate, K2Na4(WO4)3.14H2O, has been obtained by Ullik, whilst Hallopeau describes a tungstate of potassium and tungsten, of composition K2O.WO2.4WO3, prepared by heating potassium paratungstate with tin for one hour at a temperature sufficiently high to melt the tungstate. On treating the residue successively with boiling water, concentrated hydrochloric acid, boiling potassium carbonate (50 per cent, solution), and finally hot water, the compound is obtained as dark blue prismatic crystals.


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