Question

A large flask fitted with a stopcock is evacuated and weighted. Its mass is found to be 134.567 g. It is then filled at a pressure of 735 mm and `131^(@)C` with a gas of unknown molecular mass and then reweighed. Its mass is 137.456 g. The flask is then rewighed. Its mass weighted again, its mass is now 1067.9 g. Assuming that the gas is ideal, calculate the molar mass of the gas.

Answer 1

Mass of water filling the flask is
`(10.67.9-134.567)g=933.333g`
`therefore` volume of flask=volume of water filling the flask ltbr `=933.3cm^(3)`
`(therefore` density of `H_(2)O=1gcm^(-3)`)
Now `P=735mm`, `T=31+273K=304K`
`V=933.3cm^(3)`
applying `PV=nRT`
`((735)/(760)atm)((933.3)/(1000)L)=nxx0.0821xx304`
gives `n=0.036mo`
Mass of 0.036 mol of the gas `=(137.456-134.567)g`
`=2.889g`
therefore mass of 1 mol of the gas `=(2.889)/(0.036)=80.25g` `mol^(-1)`