Question

Compound A contains 8.7% Hydrogen, 74% Carbon and 17.3% Nitrogen. The molecular formula of the compound is,
Given : Atomic masses of C, H and N are 12, 1 and 14 amu, respectively. 
The molar mass of the compound A is 162g mol^–1.

• A. C₄H₆N₂
• B. C₂H₃N
• C. C₅H₇N
• D. C₁₀H₁₄N₂

Answer 1

The Correct Option is D

To determine the molecular formula of Compound A, we'll follow these steps:

1. Determine the empirical formula of the compound.
2. Calculate the empirical formula mass.
3. Use the molar mass to find the molecular formula.

Step 1: Calculate the Empirical Formula

Given percentages by mass for each element in Compound A are:

• Hydrogen (H): 8.7%
• Carbon (C): 74%
• Nitrogen (N): 17.3%

Convert these percentages to moles using the atomic masses:

• Moles of C = \frac{74}{12} \approx 6.17
• Moles of H = \frac{8.7}{1} = 8.7
• Moles of N = \frac{17.3}{14} \approx 1.24

Find the simplest whole number ratio by dividing each by the smallest number of moles:

• Relative moles of C: \frac{6.17}{1.24} \approx 5
• Relative moles of H: \frac{8.7}{1.24} \approx 7
• Relative moles of N: \frac{1.24}{1.24} = 1

Thus, the empirical formula is C₅H₇N.

Step 2: Calculate the Empirical Formula Mass

The empirical formula mass is:

• C: 5 × 12 = 60
• H: 7 × 1 = 7
• N: 1 × 14 = 14

Total empirical formula mass = 60 + 7 + 14 = 81 g/mol.

Step 3: Determine the Molecular Formula

Given molar mass of Compound A is 162 g/mol. Find the ratio of the molar mass to the empirical formula mass:

\text{Ratio} = \frac{162}{81} = 2

The molecular formula is thus twice the empirical formula: C₁₀H₁₄N₂.

Conclusion: The correct molecular formula of Compound A is C₁₀H₁₄N₂, which matches option D.