Question

One mole of hydrocarbon consumed 4.5 moles of oxygen for complete combustion and gave equal volumes of ${\mathrm{CO}}_2$and water vapour. Identify the formula of the hydrocarbon.

• A. ${\mathrm{C}}_3{\mathrm{H}}_4$
• B. ${\mathrm{C}}_2{\mathrm{H}}_4$
• C. ${\mathrm{C}}_3{\mathrm{H}}_8$
• D. ${\mathrm{C}}_3{\mathrm{H}}_6$

Answer 1

Answer: (A), (D)

${\mathrm{C}}_3{\mathrm{H}}_6$

Explanation of correct option:

• From the information given in the question, we can say that there are 9 $\mathrm{O}$ atoms on the reactant side.
• To make it equal to the product side and also the volumes of ${\mathrm{CO}}_2$and water vapor are equal, then 3 mol of each will be produced on the product side.
• This can be clearly understood from the balanced reaction below:

$\underset{\mathrm{Propene}}{{\mathrm{C}}_3{\mathrm{H}}_6\left(\mathrm{g}\right)}+\underset{Oxygen}{\frac{9}{2}{O}_2\left(g\right)}\to \underset{\mathrm{Carbon}\mathrm{dioxide}}{3{\mathrm{CO}}_2\left(\mathrm{g}\right)}+3\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)}$

The molecular formula of the hydrocarbon is ${\mathrm{C}}_3{\mathrm{H}}_6$.

Hence, the correct option is (D).