Question
Establish the relation between molecular weight and vapour density.
Answer
From the definition of vapour density, we know,
Vapour density (VD) = (Mass of (v) volume of gas)/Mass of (v) volume of hydrogen
(At the same temperature and pressure)
According to Avogadro’s hypothesis at the same temperature and pressure equal volume of any gas contains an equal number of molecules.
∴ Vapour density (VD) = n-molecules of gas/n-molecules of hydrogen
= Weight of 1 – molecule of gas/Weight of 1-molecules of hydrogen
= molecular weight of gas (M)/molecular weight of hydrogen
VD = M/2
or, M = 2D
