Question

A gaseous alkane is burnt completely in oxygen. The volume of $O_2$required for complete combustion to the volume of $C{O}_2$ formed is 7:4. Determine the formula for alkane. [Alkane is $C_n{H}_{2n+2}$]

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

In organic chemistry, you have learnt that general formula of an alkane is $C_n{H}_{2n+2}$.
When an alkane is burnt completely burnt in $O_2$,

$C_n{H}_{2n+2}+[n+\frac{n+1}{2}]O_2\to nC{O}_2+(n+1)H_{2}O\left(1\right)$

Given that $\frac{volof{O}_{2}required}{volofC{O}_{2}formed}$ = $\frac{7}{4}$

$\frac{n+\left(\frac{n+2}{2}\right)}{n}$ = $\frac{7}{4}$

n = 2

$\therefore$ The alkane is $C_2{H}_6$