Exactly of an unknown gaseous hydrocarbon was exploded with an excess of oxygen. On cooling to room — States of Matter and Gaseous State Chemistry Question
Question
Exactly $7.5\text{ mL}$ of an unknown gaseous hydrocarbon was exploded with an excess of oxygen. On cooling to room temperature, the mixture exhibited a volume contraction of $15\text{ mL}$. If the vapour density of the hydrocarbon is $14$, its molecular formula is:
Answer: D
💡 Solution & Explanation
Molar mass $M = 2 \times VD = 2 \times 14 = 28\text{ g/mol}$. Ethene ($C_2H_4$) has a mass of $28$. Verification: First contraction $= V(1 + y/4)$. For $C_2H_4$, contraction $= 7.5(1 + 4/4) = 7.5(2) = 15\text{ mL}$, which perfectly matches the data.
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