[blanny]

Hi, I'm a first year chem student and I have a question about how to set up a molecular formula problem.  I know how to do these when the mass is given, but I'm just not seeing this one that only gives volumes.  Here goes:

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When 2.0L of a gaseous compound containing only carbon, hydrogen, and sulfur was combusted in pure oxygen, 10L of CO2 gas, 12L of H20 gas, and 6.0L of SO2 gas were produced with all gases measured at the same temperature and pressure.  Determine the molecular formula of the gaseous compound.
So the unbalanced equation would be CxHySz + O2 --> CO2 + H2O + SO2

I used STP values to get the moles of CO2 to be 0.44 so moles of C would be 0.44 as well.
Moles of H20 I found to be .53 so 1.1 moles of H.
Moles of SO2 I think is .27 so .27 moles of S.

From there I tried to divide the three by the smallest moles to get whole number ratios but that wasn't working very well.  Can someone give me the method to solve the problem please?  I would really appreciate it.  I have a test tomorrow and this is the only one my study group couldn't figure out.

Thanks,

Blanny

[Borek]

You have not used information about your compound amount, you have also forgot that same volumes of gases contain same amount of molecules (whose law is it?). 2L gave 10L of CO₂, thus you have 5 carbons per molecule - and so on.

[blanny]

So would it be C5H12S2?

[Borek]

C₅ is OK, think over hydrogen (H₂O) and sulfur.

[blanny]

Thanks for your help Borek.  I got this question right on the exam. =)