Question

At 27'C, H 2 is leaked through a tiny hole into a vessel for 20 minutes.
Another unknown gas at the same T and P as that of H 2 is leaked
through the same hole for 20 minutes. After effusion of the gas, the
mixture exerts a pressure of 6 atm. The H 2 content of the mixture is 0.7
moles. If volume of the container is 3 litres what is the molecular
weight of unknown gas ?

Answer 1

P V = (n1 + n2) R T

Substituting P = 6 atm,  V = 3 litre, R = univ gas constant, T = 300 K

We get (n1 + n2).

  n1 = H2 content is 0.7 moles.

So you find the other n2 = (n1+n2) - 0.7