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Chemistry combustion analysis gas problem

  1. Nov 28, 2012 #1
    1. The problem statement, all variables and given/known data

    Complete combustion of a 0.0150 mol sample of a hydrocarbon, CxHy, gives 1.680L of CO2 at STP and 0.810g of H2O
    a) what is the molecular formula
    b) what is empirical formula

    2. Relevant equations

    pv=nRt

    3. The attempt at a solution

    a) mol of co2: n=pv/Rt=1 atm * 1.680L/0.0821*273= 0.074955495mol

    - Mol of h2o: 0.810g/18.02g/mol * 2 = 0.08990011 mol H2

    mol ratio: 0.08990011/0.074955495= 1.199379845... * 5 = 6

    molecular formula: c5h6.

    Is this wrong? is it possible to multiply by four and round the number to 5 instead of 6? so that it would be c4h5? Or is the above one correct?


    also: how do i get the molecular formula? i cant get a lowest whole number ratio here.
    Thanks!
     
  2. jcsd
  3. Nov 28, 2012 #2

    chemisttree

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    Looks good to me provided you did the math correctly. Could also be C10H12 or C15H18...
     
    Last edited: Nov 28, 2012
  4. Nov 29, 2012 #3

    Borek

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    C5H6 it is, OP started with the number of moles.
     
  5. Nov 29, 2012 #4

    chemisttree

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    Argh! That should have been Nellen's reply.
     
  6. Nov 29, 2012 #5

    Borek

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    Oops.
     
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