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Homework Help: What are the empirical and molecular formulas of the compound

  1. Aug 22, 2007 #1
    "A compound contains only carbon, hydrogen, and oxygen. Combustion of 10.68 mg of the compound yields 16.01 mg CO2 and 4.37 mg H2O. The molar mass of the compound is 176.1 g/mol. What are the empirical and molecular formulas of the compound."

    I saw an earlier post but it wasn't solved yet. There were some good explanations but can I get a step by step guide to solving this, i just cant seem to get it

    I have started off by finding the moles of CO2 and H2O but after that step i cannot find the next step. The answer to the problems are C3H4O3 and C6H8O6
    Last edited: Aug 22, 2007
  2. jcsd
  3. Aug 22, 2007 #2


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    You can work out how many moles of C and H are produced from the masses of the CO2 and H2O given, ignore the oxygen because you don't know how much came from the air.
    You know how many moles of the substance there were so you can work out how many carbon and hydrogen it had.
    You have the molecular mass so any difference between the amount of carbon and hydrogen you worked out must be oxygen.
  4. Aug 22, 2007 #3
    1) find the grams of C from CO2, find the grams of H from H2O

    2) Original amount - grams of (C + H) = Grams of O

    3) find the moles of C from CO2, H from H2O, O from molar mass of O

    4) CxHyOz ... divide by the smallest amount of moles and manipulate your findings till you have a whole number which gives you your Empirical Formula

    5) MW/EW = some value = Multiply your EF by this value.
    Last edited: Aug 22, 2007
  5. Aug 22, 2007 #4
    i just worked it ... it works, have you solved it yet?
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