Question

Carbon dioxide, CO2, was shown to effuse through a porous plate at the rate of 0.020 mol/min. The same quantity of an unknown gas, 0.020 moles, is found to effuse through the same porous barrier in 90. seconds. Calculate the molar mass of the unknown gas.

Answer 1

rate of Co2   = 0.02 mole/min

time                 = 90 sec = 90/60   = 1.5min

rate of unknown gas   = no of moles/time   = 0.02mole/1.5 min   = 0.013mole/min

molar mass of CO2   (M CO2) = 44g/mole

r CO2/r un       = M un/M CO2

0.02/0.013    = M un/44

1.54             = M un/44

squring on both sides

2.3716    = M un/44

M un     = 44*2.3716    = 104.35 g/mole

molar mass of unknown gas = 104.35g/mol