Question

An alkene occupies $0.4{\text{L g}}^{-1}$ at STP. The number of hydrogen atoms in one formula unit of the alkene is:

• A. $10$
• B. $8$
• C. $6$
• D. $12$

Answer 1

The correct option is B $8$

Volume of $1g$ of alkene $=0.4L$ at STP

$0.4L$ is the volume of $1g$ of $C_n{H}_{2n}$ gas.
$\therefore 22.4L$ of gas is the volume of 1 mol of the compound.

$\text{molar mass}=\frac{22.4}{0.4}=56g$

$\therefore 12n+2n=14n=56$
$\therefore n=4$
$\therefore$ The formula of the alkene is $C_4{H}_8$