What is the rate of effusion for this question?

Posted on 2015-12-08 07:47:00 in Physics by ALEX JEN

I don't quite understand the answer to this chemistry quesiton.

An equimolar mixture of methane (CH4) and propane (C3H8) effuses out of a container through a tiny hole. If 5.0 x 10^2 mg of CH4 effused out of the container in 1.00 hour, how many mg of C3H8 effused out in the same time? The molar masses are 1.0079g/mol for H and 12.011g/mol for C, and 1000mg = 1g.

I know there's a formula for efussion rates of 2 substance which is: (Effusion Rate A)/(Effusion Rate B) = square root (Molar Mass B/ Molar Mass A)

If we say A is C3H8 and B is CH4 then it should be Effusion Rate A/Effusion Rate B = 0.6
Then effusion Rate A = 0.6 times effusion Rate B and effusion rate of B is 500mg/hr. So the answer I got was 300mg/hr, but the solution manual says it is 829mg/hr.

What exactly am I doing wrong here and can someone work this out with the correct steps?

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