Question

An evacuated glass vessel weighs $50.0g$ when empty $148.0g$ when filled with a liquid of density $0.98gm{L}^{-1}$ and $50.5g$ when filled with an ideal gas at $760mmHg$ at $300K$, Determine the molar mass of the gas.

• A. $32.1g$
• B. $321g$
• C. $123g$
• D. $12.3g$

Answer 1

The correct option is C $123g$

Weight of liquid = $148-50=98g$
Volume of liquid =$\frac{98}{0.98}=100mL$= volume of vessel
It means, vessel of $100mL$ contains ideal gas at $760mmHg$ at $300K$
Weight of gas = $50.5-50=0.5g$
using, $PV=nRT$, where, $n=\frac{w}{m}$
So,
$PV=\frac{w}{m}RT$
Substituting the values, we get,
$\frac{760}{760}\times \frac{100}{1000}=\frac{0.5}{m}0.082\times 300$
=$123$
Molecular mass of gas $m=123g$