Question

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

[write your answer to the nearest integer]

Answer 1

Mass of ideal gas $=50.5-50=0.5$ g

Mass of liquid $=148-50=98$ g

$\text{Volume}=\frac{\text{Mass}}{\text{Density}}=\frac{98}{0.98}=100$ mL or $0.1$ L

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 $M=123.15\approx 123$ g