Question

Aqueous $NaOH{\rm{ }} + {\rm{ }}{P_4}\left( {white} \right){\rm{ }} \to P{H_3} + X$. Compound X is:
A. $Na{H_2}P{O_2}$
B. $N{a_2}HP{O_4}$
C. $N{a_2}C{O_3}$
D. $NaHC{O_3}$

Answer 1

Phosphorus has an atomic number 15. In nature, it exists in two forms white and phosphorus. Phosphorus is very reactive in nature, so it does not exist freely but it exists as tetra phosphorus molecules together.

Complete answer
Aqueous sodium hydroxide solution undergoes reaction with white phosphorus to produce phosphine and sodium hypophosphite.
aqueous $NaOH{\rm{ }} + {\rm{ }}{P_4}\left( {white} \right){\rm{ }} \to P{H_3} + X$
So here X is sodium hypophosphite. This reaction can be explained with the help of following chemical equation;
$3NaOH + 3{H_2}O + {P_4} \to P{H_3} + 3Na{H_2}P{O_2}$
The reaction of white phosphorus with aqueous solution of sodium hydroxide is an example of disproportionation reaction. Disproportionation reactions are such reactions in which the phenomenon of both the oxidation and reduction takes place with the same species i.e. the same reactant undergoes both oxidation and reduction to produce distinct products. In the reaction of phosphorus with aqueous sodium hydroxide, the phosphorus simultaneously undergoes both oxidation and reduction to give two distinct products. In the given reaction, phosphorus gets oxidized into sodium hypophosphite and as well as simultaneously gets reduced to produce phosphine. The rate of the reaction is very small i.e. reaction takes place in a long time.

**Hence, option (A), is the correct option.

Note: **
White phosphorus exists in triatomic form, so due to the presence of higher angular strain it is highly reactive. Due to its reactive nature, it is stored under water. White phosphorus will react with cold concentrated sodium hydroxide to form sodium hypophosphite and phosphine gas. But the phosphorous other form red phosphorus will not react with alkali. So, it is also a way to differentiate white and red phosphorus.