Question

When a hydrocarbon A undergoes complete combustion it requires $11$ equivalents of oxygen and produces $4$ equivalents of water. What is the molecular formula of $A$ ?

• A. $C _{11} H _8$
• B. $C _{11} H _4$
• C. $C _5 H _8$
• D. $C _9 H _8$

Answer 1

Answer: (D)

$C _{ x } H _{ y }+\left( x +\frac{ y }{4}\right) O _2 \rightarrow xCO _2+\frac{ y }{2} H _2 O$
$\frac{ y }{2}=4 \therefore y =8$
$x +\frac{8}{4}=11$
$\therefore x =9$
$\therefore$ Hydrocarbon will be$= C _9 H _8$