Oxyacids of Phosphorus

Oxyacids of Phosphorus

Hypophosphorus acid, Phosphorus acid, Orthophosphoric acid, Metaphosphoric acid, Hypophosphoric acid, Pyrophosphoric acid

Oxyacids of Phosphorus:

  1. Hypophosphorus acid - H3PO2
  2. Phosphorus acid - H3PO3
  3. Orthophosphoric acid - H3PO4
  4. Metaphosphoric acid - HPO3
  5. Hypophosphoric acid - H4P2O6
  6. Pyrophosphoric acid - H4P2O7

  1. Phosphorus acid - Orthophosphorus acid - H3PO3

    1. Phosphorus trichloride when reacted with water gives phosphorus acid.

      PCl+ 3H2 H3PO3 + 3HCl

    2. Phosphorus trioxide (P4O6) on reaction with water gives phosphorus acid.

      P4O6 + 6H2 4H3PO3


    1. Phosphorus acid disproportionates to give PH3 and H3PO4.

      4H3PO3  3H3PO+ PH3

    2. Phosphorus acid is a disbasic acid.

      H3PO3   H+ + H2PO3-

      H2PO3-   H+ HPO3-2

    3. Phosphorus acid on reaction with phosphorus pentachloride gives phosphorus oxychloride.

      H3PO+ 3PCl5  PCl+ 3POCl+ 3HCl

  2. Orthophosphoric Acid - H3PO4

    1. Phosphorus when treated with nitric acid gives H3PO4.

      P+ 20HNO3  4H3PO4 + 20NO2 + 4H2O

    2. Calcium phosphate on reaction with sulphuric acid gives H3PO4

    3. Ca3(PO4)2 + 3H2SO4  2H3PO+ 3CaSO4

    4. Phosphorus on reaction with excess of oxygen gives oxide which on further reaction with hot water gives orthophosphoric acid.

      P+ 5O2  P4O10    4H3PO4


    1. Orthophosphoric acid is a tribasic acid and forms series of salts.

      Primary phosphate - NaH2PO4

      Secondary phosphate - Na2HPO4

      Tertiary phosphate - Na3PO4

    2. 2H3PO    H4P2O7 + H2O

    3. H3PO    (HPO3)n+ H2O
      metaphosphoric acid

    4. H3PO4 on reaction with BaCland AgNO3 gives precipitate.

      3BaCl2 + 2H3PO4  Ba3(PO4)+ 6HCl
      White ppt

      3AgNO3 + H3PO4  Ag3PO4 + 3HNO3

    5. On heating H3PO4 in presence of nitric acid with ammonium molybdate, a canary yellow precipitate of ammonium phosphomolybdate is formed. (test of Po43- ion)

      H3PO+ 21HNO3 + 12(NH4)2MnO4  (NH4)3PO. 12MoO3 + 21NH4NO3 + 12H2O

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