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 reaction sequence describes the coupling of benzene diazonium chloride with aniline. In this process, benzene diazonium chloride reacts with aniline to form an intermediate (diazoaminobenzene), which then undergoes acid-catalyzed rearrangement (amino-azo rearrangement) when warmed to $40-45^{\circ}\text{C}$ to form p-aminoazobenzene. p-aminoazobenzene is a well-known yellow dye.

Step 1: Determine the chemical formula of the yellow product (X).
The product X is p-aminoazobenzene. Its structure consists of two benzene rings linked by an azo group ($-N=N-$) with an amino group ($-NH_2$) at the para position of one ring.
Chemical Formula: $C_{12}H_{11}N_3$

Step 2: Calculate the molar mass of $C_{12}H_{11}N_3$.
Molar mass $= (12 \times 12) + (11 \times 1) + (3 \times 14)$
Molar mass $= 144 + 11 + 42 = 197\text{ g mol}^{-1}$

Step 3: Calculate the percentage of nitrogen in the compound.
Mass of Nitrogen in the molecule $= 3 \times 14 = 42\text{ g}$
Percentage of N $= \left( \frac{\text{Mass of Nitrogen}}{\text{Total Molar Mass}} \right) \times 100$
Percentage of N $= \left( \frac{42}{197} \right) \times 100 \approx 21.319\%$

Rounding to the nearest integer, we get $21\%$.