Question

White phosphorus can be separated from red phosphorus by________.
A) sublimation
B) dissolving in ​\[C{S_2}\]​
C) distillation
D) heating with alkali solution

Answer 1

Hint: White phosphorus, yellow phosphorus or simply tetra phosphorus $(P_4)$ exists as molecules made up of four atoms in a tetrahedral structure. The tetrahedral association results in ring stress and instability.

Complete answer:
White phosphorus is soluble in organic solvents such as \[C{S_2}\],\[CC{l_4}\].
Red phosphorus is insoluble in such solvents.
White phosphorus is a $P_4$ molecule. It readily dissolves in $CS_2$. But red phosphorus has chain structure and does not dissolve in $CS_2$.
White phosphorus may be separated from red phosphorus through dissolving in , \[C{S_2}\],\[CC{l_4}\] ​.
There is another way by which we can separate White phosphorus from Red phosphorus which is by heating with an alkali solution.
White phosphorus reacts with caustic alkalis (NaOH and KOH). Red phosphorus does not react with caustic alkalis (NaOH and KOH).
White phosphorus is boiled with aqueous NaOH solution to obtain phosphine.
Here is the equation:
\[{P_4} + 3NaOH + 3{H_2}O \to 3Na{H_2}PO_2 + P{H_3}\]

Therefore, the correct options are b) and d).

Note: Red phosphorus may be formed by heating white phosphorus to $300^0C$ in the absence of air or by exposing white phosphorus to sunlight. Upon similarly heating, the amorphous red phosphorus crystallizes. Red phosphorus does not ignite in air at temperatures under 240^0C.