Methane (ch4) effuses through a small opening in the side of a container at the rate of 1.30 × 10 8 mol s 1. an unknown gas effuses through the same opening at the rate of 5.42 × 10 9 mol s 1 when maintained at the same tem- perature and pressure as the methane. determine the molar mass of the unknown gas.

Answer : The molar mass of unknown gas is 92.0 g/mol

Solution :

According to the Graham's law, the rate of effusion of gas is inversely proportional to the square root of the molar mass of gas.

or,

      ..........(1)

where,

= rate of effusion of methane gas =

= rate of effusion of unknown gas =

= molar mass of methane gas  = 16 g/mole

= molar mass of unknown gas = ?

Now put all the given values in the above formula 1, we get:

Therefore, the molar mass of unknown gas is 92.0 g/mol

the answer is definitely c.