Question

For complete combustion of 5 L of an alkane, 25 L of oxygen is required. Which of the following is the alkane, if all volumes are measured at constant temperature and pressure?

• A. Isobutane
• B. Ethane
• C. Butane
• D. Propane

Answer 1

Answer: (D)

Combustion of Hydrocarbon
$C_{x}H_{y}+\left(x + \frac{y}{4}\right)O_{2} \rightarrow x \, CO_{2}+\frac{y}{2}H_{2}O$
$\therefore n \, \propto v \, \left(\right.P,T=Constant\left.\right)$
$for \, 1 \, mole \, of \, CxHy=\left(x + \frac{y}{4}\right)$ $O_{2}Required$
$for \, 5 \, litre \, of \, CxHy=\left(x + \frac{y}{4}\right)5 \, litre \, \, \, O_{2}Required$
$\therefore ratio \, of \, alkane \, \& \, O_{2} \, is \, 5/25$
$So.\left(x + \frac{y}{4}\right)5=25$
$x+\frac{y}{4}=5$
$which \, is \, satisfied \, by \, C_{3}H_{8}$