Question

A sample of oxygen gas (o2) was found to effuse at a rate equal to three times that of an unknown gas. the molecular weight of the unknown gas is ________ g/mol.

Answer 1

Answer:
              288 g.mol⁻¹

Data Given:

Rate of Effusion of O₂  =  Rₐ  =  3

Rate of Effusion of Unknown  =  Rₓ  =  1

Molecular Mass of Oxygen  =  Mₐ  =  32 g.mol⁻¹

Molecular Mass of Unknown  =  Mₓ  =  ?

Formula Used,
                             Rₐ / Rₓ  =  $\sqrt{Mx/Ma}$

Putting Values,
                             3 / 1  =  $\sqrt{Mx/32}$
Or,
                             (3 / 1)²  =  ( $\sqrt{Mx/32}$ )²

                             9 / 1  =  Mx / 32

                             Mx  =  288 g.mol⁻¹