Question

An evacuated glass vessel weighs 50 g when empty, 148 g when filled with a liquid of density 0.98 g/ml and 50.5 g when filled with an ideal gas at 760 mm Hg at 300 K. Determine the molecular weight of the gas.

• A. 123 g/mol
• B. 321 g/mol
• C. 1.23 g/mol
• D. 1235 g/mol

Answer 1

The correct option is A 123 g/mol

Mass of liquid $=148-50=98$ g
Volume of liquid $=\frac{98}{0.98}=100$ ml
Volume of vessel = Volume of liquid
Mass of gas $=50.5-50=0.5$ g
$PV=\frac{W}{M}RT$ or, $\frac{760}{760}\times \frac{100}{1000}=\frac{0.5}{M}\times 0.0821\times 300$
$\Rightarrow M=123.15\cong 123$ g