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Author Topic: Graham's law/emperical formula problem  (Read 5045 times)

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optimusprimer

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Graham's law/emperical formula problem
« on: December 05, 2007, 03:48:09 PM »

Here's the Problem: A compound contains only C,H, and N, It is 58.51% C and 7.37% H by mass.  Helium effuses through a porous frit 3.2 times as fast as the compound does. Determinine the emperical and molecular formulas of this compound.

What I have so far:
.5851 g C = .04876 moles
.0737 g H = .0737 moles
.3412 g N = .02437 moles
emperical formula = C3H2N6
emperical mass    = 122 g/mole

3.2R/R=sqrt(mm/4)
This gives me a molar mass of only 41 g/mole.
I know this can't be possible because it is less than the emperical molar mass.  Can someone try to help me and see where I went wrong?
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Sev

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Re: Graham's law/emperical formula problem
« Reply #1 on: December 05, 2007, 04:27:59 PM »

Your empirical formula is wrong.
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optimusprimer

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Re: Graham's law/emperical formula problem
« Reply #2 on: December 05, 2007, 04:37:33 PM »

Oh, I see now.  The emperical formula should be C2H3N, correct?  This would make the molecular formula C2H3N too I guess.  I don't really know how I screwed that up, but thanks for pointing out the problem.
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Sev

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Re: Graham's law/emperical formula problem
« Reply #3 on: December 05, 2007, 04:40:57 PM »

Quote
Oh, I see now.  The emperical formula should be C2H3N, correct? 

Yep  :)
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