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Homework Help: Calculate the moles of oxygen gas

  1. Oct 13, 2011 #1
    1. The problem statement, all variables and given/known data

    Calculate the number of moles of oxygen gas produced from the completely catalyzed decomposition of 6.60ml sample of a 3.5% solution of H2O2. The density of the 3.5% solution of H2O2 is 1.01 g/ml.

    2. Relevant equations
    2(H2O2) --> 2(H2O) + O2

    3. The attempt at a solution
    I used. 1.01g/ml=m/6.6ml to get 6.1206g of the solution
    Multiplied 6.1206 by .035 to get .214221g H2O2
    .214221g H2O2(1mol H2O2/18.016g H202)(2 mol O/2mol H2O2)(16g O/1 mol O) yields .1897g O
    .1897g O (1 mol O/16g O) yields .0118 mol O. This answer was rejected. I even tried .0236 since the equation shows O2, just to be sure. Wrong as well.
  2. jcsd
  3. Oct 13, 2011 #2


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    Science Advisor

    If O is 16 g/mole, and H is 1 g/mole then H2O2 is ??? g/mole? Not 18.016.
  4. Oct 14, 2011 #3
    Right, I caught that. It should be 34.016g. I ran the same calculations with that number, but to no avail.
    There was also actually 6.666g of solution, but what I've tried with that number is still wrong.
  5. Oct 14, 2011 #4


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    Staff: Mentor

    Please show your results now - there are several problems with the way you calculated amount of oxygen, but as you corrected some of them it is not clear what is the current version of your calculations, so it is not possible to check it.

    Moles of oxygen gas means moles of O2. But

    this is wrong - 0.0118 mol of atomic O is not equivalent to 0.0236 moles of O2.

    It is also possible system rejects answer that is technically correct, but has wrong number of significant digits.
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