Question

An alkene occupies $0.8{\text{L g}}^{-1}$ at STP. Thus, the total number of atoms of carbon and hydrogen in one formula unit are:

• A. $10$
• B. $8$
• C. $6$
• D. $12$

Answer 1

The correct option is C $6$

Volume of $1g$ alkene $=0.8L$ at STP

$0.8L$ is the volume of $1g{C}_n{H}_{2n}$ gas.
$\therefore 22.4L$ of gas is the volume of 1 mole of the compound $=\frac{22.4}{0.8}=28.0g=\text{molar mass}$

$\therefore 12n+2n=14n=28$
$\therefore n=2$
$\therefore$ Number of atoms of carbon and hydrogen in $C_n{H}_{2n}=C_2{H}_4=2+4=6$