At STP, `250cm^(3)` of a gas weighs 0.7317g. If the density of `H_(2)` gas at STP be 0.08987`g*L^(-1)` then what will be the vapour density of the gas? Determine the molecular mass of the gas.

Explanation

Mass of 250 `cm^(3)` of `H_(2)` gas at STP
`=(0.08987xx250)/(1000)g=0.0224g`.
[`because` At STP, the density of `H_(2)` gas=0.08987`g*L^(-1)`]
`therefore`Vapour density of the gas
`=("mass of 250 "cm^(3)" gas at STP")/("mass of 250 "cm^(3)H_(2)" gas at STP")=(0.7317)/(0.0224)=32.66`
Thus, its molecular mass`=2xx32.66=65.32`.