Question

Give laboratory method for the preparation of phosphine.

Answer 1

Phosphine is a flammable, colourless, and flammable gas and has a rotten fish-like smell. It is having the formula $P{H_3}$ and known as pnictogen hydride. It is having rotten fish smell due to the presence of phosphine and disubstituted phosphane. It is prepared by both the laboratory method and the conventional method.

Complete step by step answer:
We know that phosphine can be prepared by both industrial and laboratory methods. In the laboratory method, it can be prepared by boiling white phosphorus with a solution of caustic soda in an inert atmosphere of carbon dioxide.
The phosphine obtained after this is impure. Then it is passed into an aqueous solution of hydrogen iodide. Then $P{H_4}I$ is obtained. Then it is treated with potassium hydroxide or sodium hydroxide and pure phosphine is obtained.
The reaction concerning the above processes are below as follows
${P_4} + 3NaOH + 3{H_2}O \to P{H_3} + 3Na{H_2}P{O_2}$, Here the phosphine obtained is not pure.
$P{H_3} + HI \to P{H_4}I$
$P{H_4}I + NaOH \to P{H_3} + NaI + {H_2}O$, Here the phosphine obtained is pure.
In this method, phosphine is obtained by hydrolyzing white phosphorus with a concentrated solution of sodium hydroxide.

Note: Phosphine is obtained on the reaction of calcium phosphide with water or dilutes hydrochloric acid. The reactions involving this are as follows
$C{a_3}{P_2} + 6{H_2}O \to 3Ca{(OH)_2} + 2P{H_3}$
$C{a_3}{P_2} + 6HCl \to 3CaC{l_2} + 2P{H_3}$
It is the best-known hydride of phosphorus. It is created in soil by the bacterial decline of phosphates. It is a compound that belongs to the group of organophosphorus compounds.
It is soluble in water and insoluble in organic solvents. It burns in air to form phosphorus pentoxide. It is used in semiconductor industries and Holme’s signal due to its property of spontaneous combustion.