Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Needing help

  1. Sep 26, 2005 #1
    An unknown alcohol is analyzed by combustion. When a 1.50 gram sample of the compound (containing C, H, and O) is burned, 3.30g of CO2 and 1.80g of H20 are produced. Determine the empirical formula of the compound.

    What I did was find the number of grams of Carbon and Hydrogen that are produced by using their respective percents. Then I subtracted those numbers from the total produced to get the number of grams of O in the original. I thought that the LCM(cons. of mass) allowed me to do this, but I don;'t think that it is right--can someone please help me figure out how to do this(BTW, the answer I got was C3H8O)
  2. jcsd
  3. Sep 28, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I can't follow how you got the answer. And you certainly can't find the O in the hydrocarbon because the combustion uses oxygen from air, and you don't know how much of that is used.

    Divide the weights of CO2 and H2O to find the number of moles of each. You'll find that these numbers are in the ratio 3:4. That will lead you to the answer.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook