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Mass fraction problem!

  1. Dec 2, 2008 #1
    1. The problem statement, all variables and given/known data
    If 100 g H2O contains 11.2 g H, what mass of water could be obtained from 3.06 g H2(g) reacting with an excess of O2(g)?

    2. Relevant equations
    Mass % of X in a sample= (Mass of X in sample/ Mass of the sample)*100

    3. The attempt at a solution
    The parts that confused me were 11.2g of H and the 3.06g H2. Why aren't both be H2 or H? Can anyone help me with this problem? THank you in advance.

    This is my effort:
    I look for the mass fraction of H in 100g of H2O:
    11.2g of H/100g H2O= .112

    Then, I find the Mass of H2O
    3.06g/.112 = 27.3g H2O

    Is this correct?
  2. jcsd
  3. Dec 3, 2008 #2


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    Staff: Mentor

    Is mass of 3.5 g of H different from the mass of 3.5 g H2? Do they differ in number of atoms of hydrogen?

  4. Dec 3, 2008 #3
    No, they are not the same. I understand it now.

    Thank you Borek!
  5. Dec 4, 2008 #4


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    Staff: Mentor

    Oops, not good. They ARE the same and they DON'T differ in terms of the number of hydrogen atoms.
  6. Dec 4, 2008 #5
    Oh, Thanks again :)
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