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  Inorganic Chemistry

OXIDES OF PHOSPHORUS :

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Phosphorus is quite reactive and forms number of compounds in oxidation states of –3 , +3 and +5. Phosphorus forms two common oxides namely, (a) phosphorus trioxide ( P4O6 ) and (b) phosphorus penta oxide ( P4O10 ) .
(a) Phosphorus (III) oxide ( P4O6 ):
Phosphorus trioxide.JPG
It is formed when P is burnt in a limited supply of air, P4 + 3O2 → P4O6 .
                                                                                                                                      (limited)

It is a crystalline solid with garlic odor. It dissolves in cold water to give phosphorous acid,

PO6 + 6H2O → 4H3PO3, It is therefore, considered as anhydride of phosphorus acid.
               cold           phosphorousacid

With hot water, it gives phosphoric acid and inflammable phosphine,

P4O6 + 6H2O (hot) → 3H3PO4 + PH3
                                            Phosphoric acid

It reacts vigorously with CI2 to form a mixture of phosphoryl chloride and meta phosphoryl chloride.

P4O6 + 4CI2 → 2POCI3 + 2PO2CI

(b) Phosphorus (V) oxide ( P4O10 ):

Phosphorus pentoxide.JPG

It is prepared by heating white phosphorus in excess of air, P4 + 5O2 ( excess ) → P4O10 . It is snowy white solid. It readily dissolves in cold water forming metaphosphoric acid.

P4O10 + 2H2O → 4HPO3 . With hot water, it gives phosphoric acid, .
                  (cold)        Metaphosphoric acid

P4 O10 + 6H2O → 4H3PO4 . P4O10 is a very strong dehydrating agent.
                     Hot           Phosphoric acid

It extracts water from many compounds including H2SO4 and HNO3 ,

                P4O10                                           P4O10
H2SO4 ———→ SO3 ; 2HNO3 ———→ N2O5
                      - H2O                                    - H2O

                        P4O10
CH3CONH2 ————→ CH3CN
Acetamide              -H2O           Methyl cyanide

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