Phosphorus oxoacids are oxoacids of phosphorus. Phosphorus exhibits oxidation states from +1 to +5. Oxygen may be in oxidation state -2 or -1, depending on whether a compound contains the peroxide group.
There are a large number of such compounds, some of which cannot be isolated and are only known through their salts.
Examples of phosphorus acids include:
Phosphorus oxoacids containing P in oxidation state +1:
H3PO2 (or H2PO(OH)), Hypophosphorous acid or phosphinic acid, a monoprotic acid
Phosphorus oxoacids containing P in oxidation state +3:
H3PO3 (or HPO(OH)2), Phosphorous acid or phosphonic acid, a diprotic acid
Phosphorus oxoacids containing P in oxidation state +5 (see also phosphoric acids and phosphates):
H3PO4 (or PO(OH)3), Phosphoric acid, a tribasic acid
A similar compound is peroxomonophosphoric acid H3PO5 (or OP(OH)2(OOH)), a tribasic acid containing a peroxide group that replaces an oxygen atom in the hydroxyl group
H4P2O7 (or (OH)2(O)P-O-P(O)(OH)2), Pyrophosphoric acid, a tetraprotic acid
H5P3O10 (or (OH)2(O)P-O-P(O)(OH)-O-P(O)(OH)2), Triphosphoric acid, a pentaprotic acid
H3P3O9 (or (HPO3)3, (P(O)(OH)-O-)3), Trimetaphosphoric acid, a triprotic acid
Phosphorus oxoacids containing P in oxidation state +4:
H4P2O6 (or (OH)2P(O)−P(O)(OH)2), Hypophosphoric acid, a tetraprotic acid
Phosphorus oxoacids containing P in mixed oxidation states:
H4P2O6 (or H(OH)(O)P-O-P(O)(OH)2), Isohypophosphoric acid, a tetraprotic acid and isomer of hypophosphoric acid, containing P in oxidation state +3 and +5
