Question

A gaseous hydrocarbon gives upon combustion 0.72 g of water and 3.08 g of $CO_{2}$ . The empirical formula of the hydrocarbon is

• A. $C_{6}H_{5}$
• B. $C_{3}H_{4}$
• C. $C_{2}H_{4}$
• D. $C_{7}H_{8}$

Answer 1

Answer: (D)

$C_{x}H_{y}+\left(x + \frac{y}{4}\right)O_{2} \rightarrow xCO_{2}+\frac{y}{2}H_{2}O$
Number of moles of $CO_{2}=\frac{3.08}{44}=0.07$
So $x=0.07$
Number of moles of $H_{2}O=\frac{0.72}{18}=0.04$
So $y=0.08$
$x:y=7:8$
Therefore, empirical formula of hydrocarbon is $C_{7}H_{8}$ .