Question

Phosphorus on reaction with $NaOH$ produces $P{H}_3$ and $Na{H}_{2}P{O}_2$, This reaction is an example of:

• A. oxidation
• B. reduction
• C. disproportionation
• D. displacement

Answer 1

Answer: (C)

disproportionation

Given that:

$P_4+3NaOH+3H_{2}O\to 3Na{H}_{2}P{O}_2+P{H}_3$

assigning the oxidation number on $P$ in each molecule by considering oxidation number of $H=+1,O=-2,P_4=0$ we get oxidation state as:

$\stackrel{0}{P_4}+3NaOH+3H_{2}O\to 3Na{H}_2\stackrel{+1}{P}{O}_2+\stackrel{-3}{P}{H}_3$

In the reaction oxidation state of $P$ changes from 0 to +1 and -3,,simultaneous as:

$\stackrel{0}{P_4}\to Na{H}_2\stackrel{+1}{P}{O}_2$

$\stackrel{0}{P_4}\to \stackrel{-3}{P}{H}_3$

Thus its a disproportionation reaction which is defined as a redox reaction in which a compound of intermediate oxidation state converts to two different compounds, one of higher and one of lower oxidation states.