Question

Give the disproportionation reaction of $H_{3}P{O}_3$.

Answer 1

Disproportionation is a type of redox reaction where an element from a reaction undergoes both oxidation and reduction to form two different types of products.

Orthophosphorous acid (or phosphorus acid) disproportionates to produce orthophosphoric acid (or phosphoric acid) and phosphine on heating.

$4H_{3}P{O}_3\stackrel{Heat}{\to }3H_{3}P{O}_4+P{H}_3$
Phosphorus Phosphoric Phosphine
acid acid

Thus $H_{3}P{O}_3$ (oxidation state +3) oxidizes to give $H_{3}P{O}_4$ (oxidation state +5) and reduced to produce phosphine (oxidation state -3).

Each element undergoes oxidation and reduction:

Oxidation half-reaction ( Charge of P has increased +3 to +5 )
$H_{3}P{O}_3\stackrel{Heat}{\to }{H}_{3}P{O}_4$

Reduction half reaction ( Charge of P has decreased +3 to -3 )
$H_{3}P{O}_3\stackrel{Heat}{\to }P{H}_3$