Question

Give the disproportionate reaction of ${{H_3}{PO_3}}$:

Answer 1

Hint: The two products formed in the disproportionation reaction have different oxidation states of which the reactant oxidation state is in intermediate between the two.

Complete answer:
Disproportionation reaction is a type of redox reaction in wh9ch two products are formed from a single compound. The products formed are by both oxidation reaction and reduction reaction but simultaneously, at the same time. Before putting the disproportionation reaction of phosphorous acid, let us get to know what reduction and oxidation reactions are.
Reduction – It is a process of addition of electrons to a species which lacks electrons or reduction also means addition of hydrogen from a compound or removal of oxygen from it. A compound which reduces other chemical species is called reducing agent.
Oxidation – We can say it is the reverse of the reduction process. In oxidation addition of oxygen generally occurs or removal of electrons or removal of hydrogen is called oxidation. The species which oxidizes the other reacting species is known as oxidizing agent.
In disproportionation reaction, the reactant species itself undergoes both oxidation and reduction to give two different products. As mentioned in the question, phosphorous acid ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{3}}}$ upon heating undergoes disproportionation reaction to give phosphoric acid ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{4}}}$ and phosphine ${\text{P}}{{\text{H}}_{\text{3}}}$. Let us give the equation ${\text{4}}{{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{3}}}\xrightarrow{\Delta }{\text{3}}{{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{4}}} + {\text{P}}{{\text{H}}_{\text{3}}}$ . The oxidation state of phosphorus in the reactant is +3 while in phosphoric acid it is +5 and in phosphine it is -3, this proves the simultaneous oxidation and reduction.

Note:
When the oxidation number of phosphorus increased from +3 to +5 , there was a loss of electrons this occurred by oxidation. And when it changes from +5 to -3 the state is decreased which means the reaction is reduced.