A large flask fitted with a stop-cock is evacuated and weighted, its mass is found to be 134.567 g. It is then filled to a pressure of 735 mm at `31^(@)C` with a gas of unknown molecular mass and then reweighed, its mass is 137.456g. The flask is then filled with water and weighed again, its mass is now 1067.9g. Assuming that the gas is ideal, calculate the molar mass of the gas.

Answer

A, B

Explanation

Mass of water filling the flask `=(1067.9-134.567)g=933.333 g`
`:.` Volume of flask =Volume of water filling the flask`=933.3 cm^(3)" " (`:'` "density of "H_(2)O=1 g cm^(-3))`
Now, P=735 mm, T=31+273 K=304K, V`=933.3 cm^(3)`
Applying PV=nRT, i.e., `((735)/(760)atm)((933.3)/(1000)L)=nxx0.0821 L atm K^(-1)mol^(-1)xx304 K`
This gives n=0.036 mol
Mass of 0.036 mol of the gas =(137.456-134.567) g=2.889 g
`:.` Mass of 1 mol of the gas `=(2.889)/(0.036)=80.25 g`