What is the molar mass of the unknown gas?

Question

Tetrafluoroethylene (C₂F₄) effuses at a rate of 4.6×10^-6 moles per hour. An unknown gas effuses at a rate of 6.5×10^-6 moles per hour under identical conditions.

Answer 1

rate 1/rate 2 = sqrt MW 2/sqrt MW 1

MW C2F4 = 62 g/mol

MW unknown = x

4.6/6.5 = sqrt x/sqrt 62

square both side...

0.500 = x/62

x = 31 g/mole