Chemical elements
    Physical Properties
    Chemical Properties
      Hydrogen Selenide
      Selenium Fluorides
      Selenium Monochloride
      Selenium Tetrachloride
      Selenium Monobromide
      Selenium Tetrabromide
      Selenium Chlorobromides
      Selenium Oxyfluoride
      Selenium Oxychloride
      Sulphur Selenium Oxytetrachloride
      Selenium Oxybromide
      Chloroselenic Acid
      Selenium Dioxide
      Selenious Acid
      Selenium Trioxide
      Selenic Acid
      Perselenic Acid
      Selenium Sulphoxide
      Selenotrithionic Acid
      Diselenotrithionic Acid
      Selenopentathionic Acid
      Selenium Nitride
      Nitrosylselenic Acid
      Phosphorus Subselenide
      Phosphorus Monoselenide
      Tetraphosphorus Triselenide
      Phosphorus Triselenide
      Phosphorus Pentaselenide
      Phosphorus Chloroselenide
      Selenophosphates and Oxyselenophosphates
      Carbon Diselenide
      Carbon Subselenides
      Carbon Oxyselenide
      Carbon Sulphidoselenide
      Cyanogen Monoselenide
      Cyanogen Diselenide or Selenocyanogen
      Cyanogen Triselenide
      Selenocyanic Acid
      Ammonium Selenocyanate
      Caesium Triselenocyanate
      Copper Selenocyanate
      Lead Selenocyanate
      Magnesium Selenocyanate
      Mercurous Selenocyanate
      Mercuric Selenocyanate
      Potassium Selenocyanate
      Silver Selenocyanate
      Sodium Selenocyanate
      Zinc Selenocyanate
      Silicon Selenide
    Detection and Estimation

Selenophosphates and Oxyselenophosphates

By the action of phosphorus pentaselenide on aqueous solutions of the selenides of the respective metals, selenophosphates of the alkali and alkaline earth metals and of magnesium can be prepared. The reaction takes place according to the equation:

3M2Se + P2Se5 = 2M3PSe4.

The tetraselenophosphate is not obtained in the solid state, however, being decomposed by water, thus:

M3PSe4 + H2O = M3PSe3O + H2Se.

The decomposition may go still further, the compound M3PSe2O2 or even M3PSeO3 being formed. Intermediate compounds such as K3PSe2.5O1.5 are also formed, which may be isomorphous mixtures of various oxyselenophosphates.

The oxyselenophosphates may also be prepared by the action of phosphorus pentaselenide on the hydroxides of the metals. Normal salts are only obtained in the case of the alkali metals; the alkaline earth metals give monohydrogen salts. The following oxyselenophosphates have been prepared and described:

Sodium Trioxysele no phosphate, Na3PSeO3.20H2O, obtained by the action of phosphorus pentaselenide on either sodium hydroxide or sodium hydroselenide, crystallises in needles.

Ammonium Oxytriseleno phosphate, obtained from phosphorus pentaselenide and a saturated solution of hydrogen selenide in strong ammonia, crystallises from the warm mother-liquor in leaflets having the composition (NH4)3PSe3O.10H2O. The cold mother-liquor afterwards deposits octahedra and four-sided leaflets having the composition (NH4)5H(PSe3O)2.18H2O.

Potassium Oxyselenophosphate, K3PSe2.5.O1.5.H2O, is obtained as greenish-yellow octahedra by using potassium hydroselenide.

Barium Dioxydiseleno phosphate, BaHPSe2O2.14H2O, formed when phosphorus pentaselenide is treated either with a solution of barium hydroxide or with a saturated solution of hydrogen selenide in barium hydroxide, is a white, microcrystalline powder.

Strontium Oxyselenophosphate, obtained as a light yellow precipitate by the action of phosphorus pentasulphide on strontium hydroxide and treatment of the filtrate with alcohol, has the composition SrHPSe2/3O10/3.7H2O. Using a large excess of phosphorus pentaselenide the crystals obtained are colourless and have the composition SrHPSe4/3O8/3.8H2O, which may possibly be 2SrHPSeO3.SrHPSe2O2.24H2O.

Calcium Oxyselenophosphate has been obtained in the same way, using calcium hydroxide instead of strontium hydroxide. With the smaller proportion of phosphorus pentaselenide the crystals have the composition CaHPSeO11/3.5H2O, whilst with the larger proportion their composition is CaHPSeO3.8H2O.

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