Question

A sample of neon effuses from a container in 80 seconds. The same amount of an unknown noble gas requires 163 seconds
Identify the gas.

Answer 1

I would assume a volume of 1L.
Then Ne rate = 1/80. mass = 20.3
rate unknown = 1/163. mass = ?

(1/80/1/163) = sqrt(?/20.3)
Solve for ? and identify from the periodic table.

Answer 2

Helium

Answer 3

Kr

163/80=sqrt(unknown/20.3)

Answer 4

It is Krypton.
The effusion time is inversely proportional to the molar mass of the gas. Lighter gases require less time to effuse from a container than heavier gases. Graham's law of effusion compares the rates of effusion and molar masses of two gases. Since you are given time, you should first take the inverse of time to represent a rate. The calculation of the molar mass of this gas is summarized as follows:

rateHeratexMxMx===MxMHe−−−√(rateHe)2(ratex)2×MHe(1.25×10−2s−1)2(6.14×10−3s−1)2×20.18 g/mol

Therefore, the unknown gas has a molar mass of 83.7 g/mol , which corresponds to Krypton.