Question

A hydrocarbon $C _{ x } H _{ y }$ undergoes complete combustion with required amount of oxygen to produce $CO _{2}$ and $H _{2} O$. If the ratio of masses of hydrocarbon burnt to oxygen gas consumed comes out to be $29: 104$, then value of $(x+y)$ is :

Answer 1

Hydrocarbon $C _{ x } H _{\text {y }}$ undergoes complete combustion according to the balanced chemical equation :
$C _{ x } H _{ y }+\left(x+\frac{y}{4}\right) O _{2} \longrightarrow CO _{2}+\frac{y}{2} H _{2} O$
From the above equation, it is clear that :
$\frac{\text { Mass of } C _{ x } H _{ y } \text { burnt }}{\text { Mass of } O _{2} \text { consumed }}=\frac{12 x+y}{\left(x+\frac{y}{4}\right) 32}$
But, this ratio is given as $29: 104$.
$\therefore \frac{12 x+y}{\left(x+\frac{y}{4}\right) 32}=\frac{29}{104}$
On solving, we get $x: y=2: 5$.
But, there exists no hydrocarbon with formula $C _{2} H _{5}$.
$\therefore $ Molecular formula of hydrocarbon is $C _{4} H _{10}$
$\therefore x=4, y=10$