Question

White phosphorus on reaction with NaOH gives $P{H}_3$ as one of the products. This is a?

• A. Dimerisation reaction
• B. Disproportionation reaction
• C. Condensation reaction
• D. Precipitation reaction

Answer 1

Answer: (B)

Disproportionation reaction

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

Oxidation state of P in the LHS side=0

In right side,

For $P{H}_3$,

$x+3(+1)=0$

$x=-3$

For $Na{H}_{2}P{O}_2$,

$1+2\left(1\right)+x+2(-2)=0$

Thus from 0 oxidation state there is both reduction in the oxidation no and increase in oxidation no occur.

The first reaction is a reduction and the second reaction is oxidation. Such type of redox reaction from the same molecule .i.e. one undergoes oxidation & the other undergoes reduction is called disproportion reaction.