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EEJ MAIN Chemistry QUESTION #7515
Question 1

A gaseous hydrocarbon produces 0.72 g of water and 3.08 g of CO$_2$ upon complete combustion. What is the empirical formula of the hydrocarbon?

  • $\text{C}_2\text{H}_4$
  • $\text{C}_3\text{H}_4$
  • $\text{C}_6\text{H}_5$
  • $\text{C}_7\text{H}_8$✔️
Correct Answer Explanation

Moles of H$_2$O $= \dfrac{0.72}{18} = 0.04\ \text{mol}$ → H atoms $= 0.08\ \text{mol}$

Moles of CO$_2 = \dfrac{3.08}{44} = 0.07\ \text{mol}$ → C atoms $= 0.07\ \text{mol}$

Ratio C : H $= 0.07 : 0.08 = 7 : 8$

Empirical formula: $\mathbf{C_7H_8}$ (like toluene)