Home › MCQs › EEJ MAIN Chemistry › Question #7506
Back to Questions
EEJ MAIN Chemistry QUESTION #7506
Question 1

An organic compound is analysed by the Dumas method and produces 6 moles of CO$_2$, 4 moles of H$_2$O, and 1 mole of N$_2$ gas. What is the molecular formula of this compound?

  • $\text{C}_{12}\text{H}_8\text{N}$
  • $\text{C}_{12}\text{H}_8\text{N}_2$✔️
  • $\text{C}_6\text{H}_8\text{N}_2$
  • $\text{C}_6\text{H}_8\text{N}$
Correct Answer Explanation

From the combustion data:

  • 6 mol CO$_2$ → 6 mol C atoms
  • 4 mol H$_2$O → 8 mol H atoms
  • 1 mol N$_2$ → 2 mol N atoms

So the compound contains: C$_6$H$_8$N$_2$ per formula unit from this analysis.

But wait — this gives the empirical formula per mole of compound decomposed. If 1 mole of compound gives 6 CO$_2$, 4 H$_2$O, and 1 N$_2$, then each molecule has 6 C, 8 H, and 2 N.

Molecular formula: $\mathbf{C_6H_8N_2}$. This matches aniline dimer or similar structures. However, if 2 moles of compound gave these products, then per molecule it would be C$_{12}$H$_8$N$_2$. The standard JEE interpretation gives C$_{12}$H$_8$N$_2$ (index 1).