Experiment_15_-_Nernst_equation

Experiment_15_-_Nernst_equation - 15 Applications of the...

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15 Applications of the Nernst Equation Introduction In this experiment, you will make two investigations that involve the effect of concentration on electrochemical cell potential, and therefore, involve the use of the Nernst equation. The effect of solute ion concentration is important and can be described relatively easily. For the cell reaction at 25 °C: a A ( s ) + b B + ( aq ) c C ( s ) + d D 2+ ( aq ) (1) (2) where E° cell is a constant for a given reaction and is called the standard cell potential, and n is the number of electrons in either electrode reaction. By equation 2 you can see that the measured cell potential, E cell , will equal the standard cell potential if the molarities of D 2+ and B + are both unity, or, if d equals b, if the molarities are simply equal to each other. We will carry out our experiments under such conditions that the cell potentials you observe will be very close to the standard potentials given in the tables in your chemistry text. Considering the Cu,Cu 2+ ||Ag + ,Ag cell as a specific example, the observed cell reaction would be Cu ( s ) + 2 Ag + ( aq ) Cu 2+ ( aq ) + 2 Ag ( s ) (3) For this cell, Equation 2 takes the form (4) In the equation n is 2 because in the cell reaction, two electrons are transferred in each of the two half reactions. E° would be the cell potential when the copper and silver salt solutions are both 1 M, since then the logarithm term is equal to zero.
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