Question

Show the effect of heat on the following commercially important compounds:

Phosphorus acid, $$H_3PO_3$$

Answer 1

Phosphorus acid $$(H_3PO_3)$$ on heating undergoes disproportionation reaction to form $$PH_3$$ and $$H_3PO_4$$. The oxidation numbers of $$P$$ in $$H_3PO_3$$, $$PH_3$$ and $$H_3PO_4$$ are $$+3,-3$$ and $$+5$$ respectively. As the oxidation number of the same element is decreasing and increasing during a particular reaction, then it is disproportionation reaction.

$$H_3PO_3$$ on heating disproportionates to give orthophospheric acid and phosphine. The chemical reaction is as follows;

$$4H_3PO_3\rightarrow 3H_3PO_4+PH_3$$