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Homework Help: Finding molecular formula

  1. Jun 7, 2008 #1
    1. The problem statement, all variables and given/known data

    6.0 cm^3 of a gaseous hydrocarbon was sparked with 34.5 cm^3 of oxygen. The volume of the gaseous products after cooling to room temperature was 22.5 cm^3. The volume was reduced to 4.5 cm^3 on passing the gases through aqueous potassium hydroxide. What is the molecular formula of hydrocarbon?

    2. Relevant equations

    3. The attempt at a solution

    CxHy + ( x + y/4 ) O2 ----> x CO2 + Y/2 H2O

    Is this equation correct?Do I miss out any product?

    my doubts : First, I try calculating the volume of CO2 produced and It is 18cm^3 and the volume of H2O is apparently 4.5 cm^3. What should I do next?
    How to find the volume of oxygen gas that has reacted? Should I convert them into moles by dividing the volume of room temperature? I'm confused :(
  2. jcsd
  3. Jun 11, 2008 #2


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    You have found the volume of CO2. Convert it to moles to determine 'x'. What remains is water vapor. Find the number of moles of that and determine 'y'.
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