Question

Phosphine i.e. ${\text{P}}{{\text{H}}_3}$is prepared by---
A. ${\text{C}}{{\text{a}}_{\text{3}}}{{\text{P}}_{\text{2}}}\,{\text{ + }}\,{{\text{H}}_{\text{2}}}{\text{O}}\, \to$
B. ${{\text{P}}_4}\,{\text{ + }}\,{\text{NaOH + }}\,{{\text{H}}_{\text{2}}}{\text{O}}\, \to$
C. both are correct
D. none is correct

Answer 1

${{\text{P}}_4}$is known as white phosphorous. The base hydrolysis of white phosphorus is a laboratory method for the preparation of phosphine. The phosphine is prepared by hydrolysis of phosphides of calcium.

Complete step by step answer: Phosphine is colourless gas having rotten fish like smell. It is less soluble in water and a highly poisonous gas. Phosphorus trihalide is known as phosphine. The phosphine is prepared by hydrolysis of calcium phosphite.

The reaction of calcium phosphide with water is shown as follows:

${\text{C}}{{\text{a}}_{\text{3}}}{{\text{P}}_{\text{2}}}\,{\text{ + }}\,6\,{{\text{H}}_{\text{2}}}{\text{O}}\, \to \,3\,{\text{Ca(OH}}{{\text{)}}_{\text{2}}}\,{\text{ + }}\,2\,{\text{P}}{{\text{H}}_{\text{3}}}$

The reaction of calcium phosphide with water gives phosphine and calcium hydroxide.

The phosphine can also be prepared by heating white phosphorus with concentrated sodium hydroxide. The reaction of white phosphorus with sodium hydroxide is shown as follows:

${{\text{P}}_4}\,{\text{ + }}\,3\,{\text{NaOH}}\,\,{\text{ + }}\,3\,{{\text{H}}_{\text{2}}}{\text{O}}\, \to \,{\text{P}}{{\text{H}}_{\text{3}}}\,{\text{ + }}\,\,{\text{3}}\,{\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_2}$

The reaction of white phosphorus with concentrated sodium hydroxide gives phosphine and sodium hydrogen phosphate.

The phosphine can also be prepared by the reaction of calcium phosphide with dilute acid.

So, phosphine can be prepared by the given reactions in option (A) and (B).

Thus, the correct option is (C).

Note: \ Phosphine reacts with copper sulphate to give copper phosphide and also reacts with mercury chloride to give phosphide of mercury. The phosphine obtained from hydrolysis of copper phosphide or white phosphorus is impure. It is purified by absorption on hydrogen iodide which gives the ${\text{P}}{{\text{H}}_{\text{4}}}{\text{I}}$. ${\text{P}}{{\text{H}}_{\text{4}}}{\text{I}}$on reacting with potassium hydroxide gives pure phosphine. Phosphine is used in smoke screens. Phosphine mainly used in Holme’s signal. The combustion of phosphine gives a signal.