Question

An evacuated glass vessel weighs 40.0 g when empty, 135.0 g when filled with a liquid of density 0.95 g mL-1 and 40.5 g when filled with an ideal gas at 0.82 atm at 250 K. The molar mass of the gas in g mol-1 is: (Given : R = 0.082 L atm K-1 mol-1)

• A. 35
• B. 50
• C. 75
• D. 125

Answer 1

Answer: (D)

125

Answer 2

Weight of liquid = 135.0 – 40.0 = 95.0 g
Volume of liquid=$\frac{95}{0.95}$=100ml =0.1L
Weight of gas = 0.5 g
Moles of gas$=\frac{0.5}{M}$
$PV = nRT$
$0.82×0.1=\frac{0.5}{M}×0.082×250$
$M=0.5\times250=125$ g mol-1