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

$(a)\;121\qquad(b)\;123\qquad(c)\;221\qquad(d)\;130$

Weight of Liquid = 148 - 50 = 98g
Volume of liquid = $\large\frac{98}{0.98}$ = 100mL = Volume of vessel
Thus a vessel of 100mL contains ideal gas at 760mm of Hg at 300K
Weight of gas = 50.5 - 50 = 0.5g
Using PV = nRT
$\large\frac{760}{760}\times\large\frac{100}{1000} = \large\frac{0.5}{m}\times0.0821\times300$
$\therefore$ Molecular weight of gas (m) = 123