Question

$A$ and $B$ are two identical vessels. $A$ contains 15 $g$ ethane at 1 $atm$ and 298 $K$. The vessel $B$ contains 75 $g$ of a gas $X_2$ at same temperature and pressure.

The vapor density of $X_2$ is :

• A. $75$
• B. $150$
• C. $37.5$
• D. $45$

Answer 1

Answer: (A)

$75$

$PV=nRT$

For vessel $A$ -

$1V=\left(15/30\right)\times RT\Rightarrow V=0.5RT$

For vessel $B$ -

$1\times 0.5RT=n\times RT\Rightarrow n=0.5moles$

Molecular weight of $X_2=\frac{75}{0.5}=150$

Vapour density = molar mass of gas / molar mass of $H_2$

Vapour density of $X_2=150/2.0=75$

Hence, the correct option is $A$