Question

How will you establish the relation between vapour density and molecular mass of a gas by applying Avogadro’s law?

Answer 1

Avogadro’s law:

Stating that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

Vapour density:

Density of a particular gas or vapour at the same pressure and temperature relative to that of hydrogen.

Vapour density =  (Mass of one molecule of a gas)/(Mass of 2 atoms of Hydrogen)

Since, hydrogen is a diatomic.

Vapour density =  (Mass of one molecule of a gas)/(2 ×mass of1 atom of Hydrogen)…………..(1)

Relative molecular mass =  (Mass of molecule of a substance)/(Mass of one atom of hydrogen)………………….(2)

When we compare (1) and (2) we get,

vapour density =  (Relative molecular mass)/2

or

Relative molecular mass =2× vapour density