Question

Consider the following sequence of reactions.

The percentage of nitrogen in the yellow product (X) formed is ________ %. (Nearest Integer)
(Given Molar mass in $\text{g mol}^{-1}$ H:1, C:12, N:14)

Hint:

The yellow product X is p-aminoazobenzene. Find its molecular formula and then calculate the mass percentage of nitrogen.

Answer 1

Correct Answer: 21

The yellow product formed from the reaction of benzene diazonium chloride and aniline under the given conditions (acidic medium and mild heating) is p-aminoazobenzene. This is a coupling reaction where the diazonium group acts as an electrophile and attacks the activated para position of the aniline ring.

The molecular structure of p-aminoazobenzene is $C_6H_5-N=N-C_6H_4-NH_2$.

1. Counting the atoms in the molecule:
Carbon (C): $6 + 6 = 12$ atoms
Hydrogen (H): $5$ (from first ring) $+ 4$ (from second ring) $+ 2$ (from $-NH_2$) $= 11$ atoms
Nitrogen (N): $2$ (from azo group) $+ 1$ (from amino group) $= 3$ atoms

2. Calculating total molar mass:
$(12 \times 12) + (11 \times 1) + (3 \times 14) = 144 + 11 + 42 = 197\text{ g/mol}$

3. Calculating the percentage of Nitrogen:
$$\%N = \frac{\text{Mass of Nitrogen}}{\text{Total mass}} \times 100$$
$$\%N = \frac{42}{197} \times 100 = 21.32\%$$

The nearest integer value is $21$.