Calculate the relative molecular mass and vapour density of methyl alcohol [CH3OH] if 160 g. of the alcohol on vaporization has a volume of 112 litres at s.t.p.

Weight of 112 lit of CH₃OH = 160 g [at s.t.p.]

∴ Weight of 1 lit of CH₃OH = 160\over 112

= 1.4286 g

Weight of 1 lit of H₂ = 0.09 g [at s.t.p.]

Under similar temperature and pressure,

Vapour density of gas methyl alcohol

= 1.4286\over 0.09

= 15.87 ≈ 16

Molecular weight = 2 × Vapour density

= 2 × 15.87 = 31.74 g ≈ 32 g

Hence, molecular weight of methyl alcohol is 32 g and vapour density of methyl alcohol is 16