The main oxides of phosphorus are phosphorus trioxide (P4O6) and phosphorus pentoxide (P4O10). Phosphorous trioxide is regarded as the anhydride of phosphorous acid (H3PO4). phosphorus trioxide (P4O6) is prepared by heating phosphorous in limited supply of oxygen. P4O10 is prepared by burning white phosphorous in excess of air or oxygen.
P4 + 3O2 -------------> P4O6
P4 + 5 O2 ------------> P4O10
P4O10 has great affinity for water and hence it is used as a dehydrating agent. It can dehydrate HNO3 and H2SO4 to yield N2O5 and SO3 respectively.
2H2SO4 + P4O10 ------------> 2SO3 + 4HPO3
P4O6 and P4O10 dissolves in water to give phosphorus acid and orthophosphoric acid respectively.
P4O6 + 6H2O -------------> 4H3PO3
P4O10 + 6H2O --------------> 4H3PO4
Related article oxyacids of phosphorus
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