Question

The mass of benzanilide obtained from the benzoylation reaction of \(5.8 \, \text{g}\) of aniline, if yield of product is \(82%\), is ______________ g (nearest integer).
(Given molar mass in g mol\(^{-1}\): H : 1, C : 12, N : 14, O : 16)

Hint:

In yield-based problems, always calculate the theoretical yield first using stoichiometry, then multiply by percentage yield to obtain the actual product mass.

Answer 1

Correct Answer: 10

To find the mass of benzanilide obtained, follow these steps:

1. Calculate the moles of aniline used. The chemical formula for aniline is C₆H₅NH₂. The molar mass of aniline is calculated as:
   Molar Mass of C₆H₅NH₂ = \(6 \times 12 + 5 \times 1 + 14 + 2 \times 1 = 93 \, \text{g mol}^{-1}\).
2. The moles of aniline = \(\frac{5.8 \, \text{g}}{93 \, \text{g mol}^{-1}} \approx 0.0624 \, \text{mol}\).
3. Since the reaction of aniline with benzoyl chloride produces benzanilide, and it is a 1:1 reaction, the moles of benzanilide formed = moles of aniline = 0.0624 mol.
4. The molecular formula of benzanilide is C₁₃H₁₁NO. Its molar mass is:
   Molar Mass of C₁₃H₁₁NO = \(13 \times 12 + 11 \times 1 + 14 + 16 = 197 \, \text{g mol}^{-1}\).
5. Theoretical mass of benzanilide = \(0.0624 \, \text{mol} \times 197 \, \text{g mol}^{-1} = 12.293 \, \text{g}\).
6. Actual mass with 82% yield = \(0.82 \times 12.293 \, \text{g} \approx 10.08 \, \text{g}\).
7. Rounding to the nearest integer, the mass obtained is 10 g.

This result fits the range of 10,10, confirming its correctness.