Question

An evacuated glass vessel weighs 50.0 g when empty, 148.0 g when filled with a liquid of density $0.98gm{L}^{-1}$, and 50.5 g when filled with an ideal gas at 760 mm Hg at 300 K. The molar mass of the gas(as nearest integer) is _____.

Answer 1

Mass of ideal gas $=50.5-50=0.5g$
Mass of liquid $=148-50=98g$

$Volume=\frac{Mass}{Density}=\frac{98}{0.98}=100mLor0.1L$

For the gas,
$PV=\frac{w}{M}RT$

or, $\frac{760}{760}\times 0.1=\frac{0.5}{M}\times 0.0821\times 300$

or $M=123.15\simeq 123$