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Suggest reasons why the percentage yield of this reaction was not 100%. The reaction...

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danielb77 | Valedictorian

Posted May 1, 2013 at 1:37 PM via web

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Suggest reasons why the percentage yield of this reaction was not 100%. The reaction was CuSO4. 5H2O +Fe -> Cu(s) + FeSO4(aq) (the water/ liquid was dumped out leaving the solid copper after dissolved). The percentage yield was 146%.

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ncchemist | eNotes Employee

Posted May 4, 2013 at 7:08 PM (Answer #1)

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The true percent yield of any chemical reaction can never be greater than 100%.  This would violate the conservation of mass which states that matter is neither created or destroyed.  A 146% yield would mean that more solid copper metal was created than was present in the copper sulfate starting reagent.  The reason the measured percent yield is greater than 100% is because residual water is still present in the solid copper, thus affecting the weight of the copper and throwing off the yield calculation.  In industrial chemical processes, residual water solvent is removed from a solid sample by drying it in a vacuum oven at elevated temperatures and reduced pressure (vacuum).  This is the only way in which water can be completely removed from a solid.  When this is done, then the true mass of the copper can be measured and the percent yield be determined.

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