Estimate the cell potential of a Daniel cell having 1.0 M – Cu^2+ and originally having 1.0 M – Cu^2+ after sufficient ammonia has been added to the cathode compartment to make the NH3 concentration 2

Question

Estimate the cell potential of a Daniel cell having 1.0 M – Cu^2+ and originally having 1.0 M – Cu^2+ after sufficient ammonia has been added to the cathode compartment to make the NH3 concentration 2.0 M. Given: E°_Zn2+\|Zn = –0.76 V, E°_Cu2+\|Cu = +0.34 V, Kf for Cu (NH3)4^2+ = 1 × 10^12.

Prashant Kotian · Accepted Answer

Correct answer: B. The free NH3 concentration is 2.0 M. The complex [Cu(NH3)4^2+] formed is roughly 1.0 M. Kf = [complex] / ([Cu^2+]_free * [NH3]^4) = 1.0 / ([Cu^2+]_free * 16) = 10^12. So, [Cu^2+]_free = 1 / (16 * 10^12). E_Cu = 0.34 + (0.06/2)*log(1 / (16*10^12)) = 0.34 - 0.396 = -0.056 V. E_cell = -0.056 - (-0.76) = 0.704 V. Therefore, correct answer is B.

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