It takes 32 seconds for a certain number of moles of H2 to effuse through a leak in a tank. An unknown gas was later places under the same conditions; it took 1:39 for the same number of moles to effuse. Find the molecular mass of the gas.
I set it up like this:
rate of effusion H2 (32 s)/ rate of effusion unknown (99 s) = (molar mass unknown/molar mass H2 (2.02))^.5
and ended up with
molar mass unknown^.5= .459
molar mass unknown= .211
What's wrong with what I did?
The time is not the rate. rate is L/time, or in this case, mols/time. You don't have mols so just assume any number, for example, one. Let us know if you still have problems.
Ok, I understand that. So if I were to use 1 mol, what I would have is
(1 mol/32 s)/(1 mol/99 s)= (molar mass unknown/molar mass H2)^.5
Should I get the same answer regardless of what number I use for moles, as long as I set it up like that?
right.
(1/32) and (1/99) would be the rates. It doesn't matter what number of mols you use as long as you use the same for both gases. Is that 1 min and 39 seconds; if so then that is 99 seconds.
Sorry. I see the 99 now.
4 answers