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

Finding emprical formula of compound CHON

  1. Mar 7, 2007 #1
    1. The problem statement, all variables and given/known data
    a compound contains only carbon, hydrogen, nitrogen and oxygen. Combustion of 0.157g of the compound produce 0.213g of CO2 and 0.0310g of H2O. In another experiment, it is found that 0.103g of compound produces 0.0230g of NH3. What is emprical formula of the compound. Hint: Combustion involves O2. Assume all the carbon ends up in the CO2 and Hydrogen ends up in water. Also assume the Nitrogen ends up in NH3 in second experiment

    2. Relevant equations

    3. The attempt at a solution
    x+ O2= CO2 +H2O

    0.213g CO2/ 44gCO2= 0.0048mole of CO2
    0.0310g H2O/18G H2O= 0.00172 mole of H2O
    0.023g NH3/17g NH3= 0.00135 mole NH3
  2. jcsd
  3. Mar 7, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    To start, try to express the carbon, hydrogen and nitrogen in terms of grams. You can easily convert from moles since you have already done the hard work... remember that for the nitrogen your sample size is not the same as the CH determination. Express the nitrogen as percent of total weight of the compound and then multiply the percentage by the original wt of sample used to determine CH.

    Add the mass of these three elements together. Compare the answer to the starting mass. Is it the same? What is different and why?

    Once you have determined the mass of the four elements, convert to moles and express the formula in the form:

    C(moles C) H(moles H) N(moles N) O(moles O)

    Try it from there...
    Last edited: Mar 7, 2007
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook