It takes 19.6 mins for a 10.0mL sample of an unknown gas to effuse through a pinhole.

Question

A 10.0mL sample of He, required 5.05mins. What is the molar mass of the unknown gas?

I got that you have to do :
effuse rate of He/Effuse rate of Mx = Square root of (Mx/MHe) but then im stuck here.

Thank you!!:)

Answer 1

unk = 10/19.6 = approx 0.5 mL/min
He = 10/5.05 = appxox 2 mL/min

(2/0.5) = sqrt(M/4)
Square both sides.
(4/0.25) = M/4
Now solve for M.