Question

An evacuated glass vessel weights 50.0g when empty,148.0g when filled with a liquid of density 0.98g/mL and 50.5g when filled with an ideal gas 760mm Hg at 300K. Determine the molecular weight of the gas.

Answer 1

Weight of liquid = 148 – 50 = 98g

Volume of liquid = $\frac{98}{0.98}$ = 100 ml = volume of vessel it means, vessel of 100 ml contain ideal gas at 760 mm Hg at 300 K

Weight of gas = 50.5 - 50 = 0.5g

Using, PV = nRT = $\frac{w}{m}$ RT

$\frac{760}{760}\times \frac{100}{1000}$ = $\frac{0.5}{m}\times 0.082\times 300$ [n = 0.5/m]

∴ Molecular weight of gas (m) = 123