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. $C_2H_4$
• B. $C_3H_4$
• C. $C_6H_5$
• D. $C_7H_8$

Answer 1

Answer: (D)

$C_7H_8$

Answer 2

18 g $H_2O$ contains $2g H$ $\therefore 0.72 \, g \, H_2O$ contains $0.08 \, g \, H$ $44 \, g \, CO_2$, contains $12 \, g \, C$ $\therefore 3.08 \, g\, CO_2$ contains $0.84 \, g \, C$ $\therefore \, \, \, \, \, \, \, \, C: H = \frac {0.84}{12}: \frac {0.08}{1}$ $\, \, \, \, \, = 0.07 : 0.08 = 7:8$ $\therefore$ Empirical formula $= C_7H_8$