Question

In an effusion experiment it required 40 s for a certain number of moles of a gas of unknown molar mass to pass through a small orifice into a vacuum. Under the same conditions 16 s were required for the same number of moles of O2 to effuse. What is the molar mass of the unknown gas?

Answer 1

The molar  mass  of the unknown   gas  is  200  g/mol

calculation

let  the  unknown  gas  be represented   by  Y and molar mass be represented by  MM

The  molar mass of Y  is  therefore calculated  using  

 = (time of Y/ time of O2) =√(MM  of Y/ MM of O2 formula.

where  MM of  y =?

        MM of   O2 = 32  g/mol

       time  of Y = 40 s

      time   of O2 = 16  s

40/16 =√ (MM  of Y/ 32)

2.5=√MM   of Y/32

square  both side to remove the √ sign

6.25 =MM  of Y/32

multiply both side  by 32

MM of Y  is therefore= 200 g /mol