Question: Red P can be obtained from white P by: A.Heating it with a catalyst in an inert atmosphere B.Dis...

Question

Red P can be obtained from white P by:
A.Heating it with a catalyst in an inert atmosphere
B.Distilling it in an inert atmosphere
C.Dissolving it in carbon disulphide and crystallizing
D.Melting it and pouring liquid in water

Answer 1

Solution

To answer this question, you must recall the various allotropic forms of phosphorus and their properties. White phosphorus and red phosphorus are both allotropic forms of phosphorus. White phosphorus exists as a ${P_4}$ unit while red phosphorus consists of multiple ${P_4}$ units joined together.

Complete step by step answer:
Phosphorus has three allotropic forms, namely, white phosphorous, red phosphorus and black phosphorus. All these forms are interconvertible.
White phosphorus is the most simple of all the allotropes consisting of a ${P_4}$ unit. White phosphorus is obtained when phosphate rock is heated with coke or sand in an electric furnace. It is white waxy and soft solid and can be cut with a knife. It is extremely poisonous and causes diseases like Phossy jaw to people coming in contact.
Red phosphorus is a non- poisonous, hard, crystalline and odorless solid. It has an iron grey lustre and is made up of many ${P_4}$ units joined together. Thus, we can prepare red phosphorus from white phosphorus. This conversion is achieved by heating white phosphorus at a temperature of around $573K$ in an inert atmosphere, that is, out of contact of air in presence of a catalyst. The catalyst used is either carbon dioxide gas or iodine gas.
${P_4}(white)\xrightarrow[{C{O_2}/{I_2}}]{{573K}}{P_4}(red)$

Hence, the correct answer is A.

Note:
Phosphorus is represented by the chemical symbol P. It has atomic number 15 and is a member of group 15 and period 3 of the periodic table. It is a non- metal in the p block and is highly reactive.
Phosphorus has 3 electrons in its $3p$ orbital and can thus form three bonds in the ground state. So each phosphorus forms three bonds and the molecule of phosphorus exists as ${P_4}$ . It exists in the gaseous state as white phosphorus as ${P_4}$ molecule which has a tetrahedral shape.