Question

Some standard electrode potentials at 298 K are given below:
Pb2+/Pb –0.13 V
Ni2+/Ni –0.24 V
C2+/Cd –0.40 V
Fe2+/Fe –0.44 V
To a solution containing 0.001 M of X2+ and 0.1 M of Y2+, the metal rods X and Y are inserted (at 298 K) and connected by a conducting wire. This resulted in the dissolution of X.
The correct combination(s) of X and Y, respectively, is(are)
(Given: Gas constant, R = 8.314 J K-1 mol-1, Faraday constant, F = 96500 C mol-1)

• A. Cd and Ni
• B. Cd and Fe
• C. Ni and Pb
• D. Ni and Fe

Answer 1

Answer: (A), (B), (C)

Cd and Ni

Answer 2

X + Y2+ X2+ + Y
$\begin{array}{l}E = E^{0} – \frac{0.06}{2} log_{10}\left ( \frac{10^{-3}}{10^{-1}} \right )\end{array}$
E = Eo + 0.06
(a) E° = –(– .4) + (– .24) = .16 > 0
(b) E° = –(– .4) + (– .44) = –.04 < 0 and Ecell = –0.04 + 0.06 = +0.02 > 0
(c) E° = –(– .24) + (– .13) = .11 > 0
(d) E° = –(– .24) + (– .44) = –.2 < 0
∴ Ecell = –0.2 + 0.06 = –0.14 < 0
∴ If Ecell > 0 then the cell construction is possible.