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Homework Help: Please help! Molecular formula Q

  1. Mar 23, 2006 #1
    The insecticide deildrin contains carbon, hydrogen, oxygen, and chlorin. 1.5100g sample of this compound is burned to produce 2.0938g CO2 (g) and 0.2855g H2O(g). They're half as many chlorine atoms as carbon atoms in the compound. The molar mass of the dieldrin is 381g/mole. What is the molecular formula?

    I don't know where to start on this. Can anyone give me a jumpstart? Thanks
  2. jcsd
  3. Mar 23, 2006 #2


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    How about converting the masses in moles...:smile:
  4. Mar 23, 2006 #3
    I just attempted this and got an answer of C6H4O14Cl3, but the molecular mass of that is 406 and not 381 :(.

    I'll lay out what I did anyways and maybe you can spot my mistake and be able to figure it out for yourself :).

    -convert carbon dioxide and water to moles, and then you'll be able to figure out moles of C, H, and O
    -divide by the smallest amount of moles to get decimal ratios between the elements' moles
    -then add in the moles of Cl, which is half the moles of C (given in the problem)
    -finally multiply formula to get all whole numbers
  5. Mar 23, 2006 #4
    That's actually how I started on this problem.

    The only thing is that if I calculate the mole using CO2 and H2O, the mole will be different for O. Using CO2, I got 0.095151 moles of O, but with H2O, I got 0.015847 mol of O.
    Which one is right?
  6. Mar 23, 2006 #5
    Hey, I looked up the formula for dieldrin online. The molecular formula is
  7. Mar 23, 2006 #6
    But that doesn't follow the half as much Cl as C, and that has a molecular mass of about 452 g/mol.
  8. Mar 23, 2006 #7
    Sorry, the molecular formula is

    Thanks for the help
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