Question

Nitrobenzene $(C_6H_5NO_2)\;$ can be reduced to aniline $(C_6H_5NH_2)\;$ by electrolytic reduction. The equivalent mass of nitrobenzene will be equal to $(\dfrac{{molecular{\text{ }}mass}}{n})$
What is the value of n?

Answer 1

Hint : We must know that nitrobenzene to aniline conversion by reduction is possible by electrolytic reduction method in a weakly acidic medium. In this question, we have to find out the value of n, i.e. valency factor.

Complete step by step solution :
As we know, Nitrobenzene can be reduced to aniline in the presence of metal or acid by electrolytic reduction method in a weakly acidic medium. So, as given , the electrolytic reduction reaction for nitrobenzene to aniline is in the following way:
${C_6}{H_5}N{O_2} + 6[{H^ + }] \to {C_6}{H_5}N{H_2} + 2{H_2}$
The reduction of one molecule of nitrobenzene to aniline requires 6 hydrogen atoms, so for this reaction, the valency factor or n is equal to 6.
Or we can solve this by considering the change in the oxidation number of Nitrogen atoms.
Given reaction is
${C_6}{H_5}N{O_2} + 6[{H^ + }] \to {C_6}{H_5}N{H_2} + 2{H_2}$
Nitrogen is reduced as follows,
${N^3} \to {N^{3 - }}$
Nitrogen has oxidation no of +3 in nitrobenzene whereas nitrogen has oxidation no. of -3 in aniline.
So, change in oxidation number of nitrogen is 6
Hence, We can conclude that the valency factor is n=6

Note : We must know that aniline is an important industrial chemical product. Which is used in large scale to produce polyurethane.We can produce aniline by hydrogenation of nitrobenzene with raney nickel or nickel alloy in large scale.If we prepare aniline by electrochemical reduction of nitrobenzene. We should be taken to avoid further reduction to cyclohexylamine.