Question

The molecular formula of the hydrocarbon (A) is:

• A. $C_2{H}_6$
• B. $C_2{H}_4$
• C. $C_3{H}_6$
• D. $C_3{H}_8$

Answer 1

Answer: (D)

$C_3{H}_8$

Let the formula of hydrocarbon A is $C_x{H}_y$\times.
$C_x{H}_y\left(g\right)+(x+\frac{y}{4})O_2\left(g\right)\to xC{O}_2\left(g\right)+\frac{y}{2}{H}_{2}O\left(l\right)$

$1ml(x+\frac{y}{4})mlxml$

$15ml(x+\frac{y}{4})ml15xml$

Volume of $O_2=\frac{357\times 21}{100}=75$ ml; volume of $N_2$ = 357- 75 = 282 ml

Volume of $C{O}_2$ = 327- 282 = 45 ml
$\therefore$ 15x = 45, x = 3

$\therefore \left(\begin{array}{c}15(x+\frac{y}{4})=75\\ x+\frac{y}{4}=5\end{array}\right)$
3 + $\frac{y}{4}=5$, on solving, we get y = 8.
Formula of (A) = $C_3{H}_8$