A cell potential of 0.427F is measured in an experiment where a solution contain

Question

A cell potential of 0.427F is measured in an experiment where a solution containing a 0.010 M solution of Pb(NO_3)_2 and a lead electrode is measured relative to a saturated calomel electrode (0.242 V relative to a SHE). The cell potential changes to 0.486F when the Pb(NO_3)_2 concentration is changed to 1.0 times 10^-4 M. Is this data consistent with the Nernst equation? Enough NaF is now added to the 10^-4 M solution of Pb^2+ to completely precipitate the Pb as PbF_2 and establish an equilibrium concentration of excess F' equal to 0.190 M. The new cell potential is 0.545 V. What is the K_sp of PbF_2? From the data in part b), determine the E^0value for the 1/2 cell reaction. PbF_2 + 2e^- Pb degree + 2F^-

Explanation / Answer

3. When the concentration was increased the cell potential also goes up, this is consistent with the Nernst equation.

the lnK values goes down with increasing concentration so the overall cell potential for the cell goes up.

a. PbF2 precipitation

E = Eo - 0.0592/n lnKsp

0.545 = (2.87 - (-0.13)) - 0.0592/2 lnKsp

Ksp for PbF2 = 1.05 x 10^36

b. Eo value for the given reaction

= -0.13 - 2.87

= -3.00 V

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