Explain chemical behaviour of oxoacids of phosphorus.

Explanation

The oxoacids having phosphorus in (+3) oxidation state tend to disproportionate to higher and lower oxidation states. For example, Orthophosphorus acid on heating disproportionate to give orthophosphoric acid and phosphine.
`underset(+3)(4H_(3)PO_(3)) to underset(+5)(3H_(3)PO_(4)) + underset(-3)(PH_(3))`
The acids which has P-H bond have strong reducing properties. Thus, hypophosphorus acid is a good reducing agent as it contains two P-H bonds and reduces, for example, `AgNO_(3)` to metallic silver:
`4AgNO_(3) + 2H_(2)O + H_(3)PO_(2) to 4Ag + 4HNO_(3) + H_(3)PO_(4)`
The hydrogen of P-H bonds are non-ionisable and do not give `H^+` and donot play any role in basicity. Only those hydrogen atoms which are attached to oxygen in P-OH bond are ionisable and give `H^+`. Hence `H_3PO_(4)` is tribasic, `H_3PO_3` is dibasic while `H_3PO_2` is monobasic.