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Formula of a mixed copper salt

  1. Mar 3, 2009 #1
    1. The problem statement, all variables and given/known data

    Cu2+OH-, and Br- form a mixed salt formula Cux(OH)yBrz. In an experiment to determine the values of x, y, and z in the formula of this compound, .760 g CuBr2 (223.4 g/mol) was dissolved in water and reacted with 10.22 ml 0.555M NaOH. Assume that in this reaction, all of the Cu2+ from the CuBr2 and all of the OH- from the NaOH were incorporated into the product but that not all of the Br- was used.

    Calculate the number of moles of Cu2+ and OH- in the product.



    2. Relevant equations



    3. The attempt at a solution
    10.22mL * 1/1000L * .555M NaOH = .00567 mols OH-
    I think that is right...but it's finding the moles of Cu that is stumping me.

    .760g CuBr2 * 2H2O * 1/259.4 = .00293 mol CuBr2

    Now I don't know how to get from that to mols of just Cu. I don't have a volume or anything.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Mar 3, 2009 #2

    alxm

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    Science Advisor

    2H2O? Two water molecules? Where did they come from?

    If you have a dozen bicycles, how many tires do you have? Two dozen, right?
    If you have a dozen molecules of CuBr2, how many atoms of Cu do you have? Two dozen.

    A mol is just a quantity. Like dozens.

    So if you have a mol of CuBr2 molecules, how many moles of Cu do you have?
     
  4. Mar 4, 2009 #3
    The 2H2O is because it's a hydrate.

    You kind of lost me on the dozen analogy though. If you have a dozen CuBr2 molecules wouldn't that just be a dozen Cu atoms?
     
  5. Mar 4, 2009 #4

    Borek

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    Staff: Mentor

    Yes, that's probably what alxm meant.

    Why do you think CuBr2 is hydrated? Judging from the molar mass given it is not.
     
  6. Mar 5, 2009 #5

    alxm

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    Science Advisor

    Do you know that? Typically these problems would include that information if it was needed, e.g. by writing CuBr2*2H2O.

    Whoops, my mind must've slipped. Yes, a dozen Cu and two dozen Br.
    (Typical.. screwing up a perfectly simple analogy)
     
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