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Unformatted text preview: hese three cells expanding the logarithmic
terms you will find that in each case the cell voltage can be written as a sum of four
terms. [Hint: ln (a b / c) = (ln a) + (ln b) – (ln c)] Three of them are invariant and
include the Eo's of the iron and copper half reactions along with the term that takes
the log of the copper ion concentration into account. The fourth term, however,
varies in value and involves only the log of the ratio of the iron species
concentrations, and must therefore be responsible for the voltage changes you
observed in the laboratory. Calculate the theoretical cell voltage DIFFERENCES for
the three concentration cells involving the copper and iron and compare your
experimental results with these predictions. Again you should expect only semiquantitative agreement. In separate calculations, find the cell voltage difference
between cell #3 in Part I and each of the iron containing cells of Part II.
Part II Analysis. Using the facts that a spontaneous cell reaction gives a positive
measured voltage when the red lead of the voltmeter is connected to the cathode, and that
reduction takes place at the cathode while oxidation takes place at the anode, which...
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 Spring '07
 Nasiri
 Chemistry

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