A large flask fitted with a stop-cock is evacuatedand weighed, its massis found to be 134.567 g . It is the 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.

A large flask fitted with a stop-cock is evacuatedand weighed, its mas

1.	A large flask fitted with a stop-cock is evacuatedand weighed, its massis found to be 134.567 g . It is the 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» Solution :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 `:.`MASSOF 1 mol of the gas `=(2.889)/(0.036)=80.25 g`