Question

a dry gas measuring 280ml at 305 K and 750 mm of Hg weighs 0.334g. calculate the molecular weight of the gas.

Answer 1

The molecular weight of the gas is 30.25 gram per mole.

• Let the molecular weight of the gas is M. Given volume of the gas, V = 280 ml, temperature of gas, T = 305 K , Pressure of Gas, P = 750 mm of Hg and weight of the gas, W = 0.334 g.
• Now first we have to change the units to SI units. Changing volume unit from ml to $m^{3}$ we get V = 280 ml = 0.00028 $m^{3}$
• Changing pressure unit from mm of Hg to Pascal we get P = 750 mm of Hg = 99991.77632 Pa
• Now from Ideal Gas equation we know $PV=\frac{W}{M}RT$ where R =  $Jmol^{-1}K^{-1}$
• Putting the values we get $99991.77632*0.00028 = \frac{0.334}{M} *8.314*305$
• After simplification we get M = 30.25
• Hence the molecular weight of the gas is 30.25 gram per mole.