500 ml. of a gas ‘X’ at s.t.p. weighs 0.50 g. Calculate the vapour density and molecular weight of the gas. [1 lit. of H2 at s.t.p. weighs 0.09 g].

Given, 500 ml. of gas ‘X’ at s.t.p. weighs 0.50 g

Therefore, 1000 ml of gas ‘X’ at s.t.p. will weigh (0.50 x 2) g

Vapour density of gas X

= Wt\ of\ 1000\ ml\ of\ gas\ at\ STP\over Wt\ of\ 1000\ ml\ of\ H_2\ at\ STP

= 0.50 × 2\over 0.09

$=11.1$

Hence, vapour density of gas is 11.11

Molecular weight = 2 × Vapour density

= 2 x 11.1

= 22.2 g

Hence, molecular weight of gas is 22.2 g