2CLabManual201303

Hint ln a b c ln a ln b ln c three of them

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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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