Chemical elements
  Tellurium
    Isotopes
    Energy
    Production
    Physical Properties
    Chemical Properties
    Physiological_Action
    Atomic Weight
    Alloys
    Detection
    Estimation
    Compounds
      Hydrogen Telluride
      Tellurium Tetrafluoride
      Tellurium Hexafluoride
      Tellurium Oxyfluorides
      Tellurium Dichloride
      Tellurium Tetrachloride
      Tellurium Perchlorate
      Tellurium Dibromide
      Tellurium Tetrabromide
      Tellurium Oxybromides
      Tellurium Tetra-iodide
      Tellurium Monoxide
      Tellurium Dioxide
      Tellurites
      Tellurium Trioxide
      Telluric Acids
      Tellurates
      Tellurium Disulphide
      Tellurium-Sulphur Sesquioxide
      Tellurium Sulphates
      Telluropentathionic Acid
      Tellurium Nitride
      Tellurium Nitrite
      Basic Tellurium Nitrate
      Carbon Sulphidotelluride
      Tellurium Dicyanide
    Application
    PDB 1el7-4fon

Tellurium Tetrafluoride, TeF4






Tellurium Tetrafluoride, TeF4, is formed by the action of fluorine on tellurium, the heat of the reaction causing the mass to become incandescent.

By dissolving tellurium dioxide in hydrofluoric acid and concentrating the solution, a tellurium oxyfluoride separates, which, according to Berzelius, yields on heating first water and then a sublimate of the tetrafluoride. Metzner, by cooling the solution to about -50° C., obtained crystals to which he assigned the formula TeF4.TeO2.2H2O, and on treating the mother-liquor with anhydrous hydrofluoric acid and cooling to -70° C., it solidified. On allowing the temperature to rise once more, the portion which remained unfused at -28° C. was regarded as tellurium tetrafluoride. Prideaux and Millott, however, using anhydrous hydrogen fluoride throughout, have not been able to obtain the tetrafluoride by such means. These investigators obtained a liquid which, in a vacuum desiccator, yielded a mass of white crystals of composition TeF4.TeO2.H2O.

Tellurium tetrafluoride is a deliquescent solid which is decomposed by water, forming tellurous acid. The foregoing method of preparation is therefore dependent on the reversibility of the reaction

TeF4 + 3H2OH2TeO3 + 4HF.

The presence of tellurite makes a special method necessary for the estimation of the fluoride, and it is found that after hydrolysis the hydrogen fluoride may be titrated with alkali, using p-nitrophenol as indicator, the end-point not being affected by the presence of tellurous acid.

Tellurium tetrafluoride combines with the fluorides of the alkali metals (including ammonium) and barium fluoride, producing colourless crystalline salts of the general formula XF.TeF4, in which X represents the equivalent weight of the metal.


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