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Homework Help: Greater than 100 percent yield (102%)

  1. Oct 2, 2012 #1
    1. The problem statement, all variables and given/known data

    Cu(s) + 4 HNO3 (aq) Cu(NO3)2 (aq) + 2 NO2 (g) + 2 H2O (l)
    Cu(No3)2 + 2NaOH -------> Cu(OH)2 + 2NaNO3
    Cu(OH)2→CuO + H2O
    CuO + H2SO4 -> H2O + CuSO4
    CuSO4(aq) + Zn ( s) ------- ZnSO4 (aq)+ Cu(s)

    I carried out the follow reactions using copper as an inital product and my percent yield was higher than 100% but I've got some possible error sources. The aqueous solutions which could have possibly remained due to poor decantation are ZnSO4 and NaNO3 and because these substances have high boiling point, they would not be removed when drying the copper using a steam bath and their masses would have an effect? I feel that this is unlikely because we used four washes in which zinc sulfate and sodium nitrate are soluble.

    We used methanol and acetone washes right beofre drying the copper and perhaps methanol remained when weighing (because acetone is more volatile)?

    In addition, would the highest possible percent error be 2%?
  2. jcsd
  3. Oct 3, 2012 #2


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    Gold Member

    Which product are you asking for?
  4. Oct 3, 2012 #3
  5. Oct 3, 2012 #4


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    Staff: Mentor

    There is no such thing as the "highest possible percent error" - error is proportional to the experimentalist clumsiness, and unlimited :wink:

    My bet is that your copper is contaminated with solid zinc. Hard to tell not knowing the complete procedure you followed.
  6. Oct 3, 2012 #5


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    Gold Member

    Probably Copper is just made a thin layer of precipitation on Zinc piece. Try using finely divided Zinc dust.
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