Question

Some standard electrode potentials at 298 K are given below:

Pb+2/Pb	−0.13 V
Ni+2/Ni	−0.24 V
Cd+2/Cd	−0.40 V
Fe+2/Fe	−0.44 V

To a solution containing 0.001 M of X⁺² and 0.1 M of Y⁺², the metal rods X and Y are inserted (at 298 K) and connected by a conducting wire. This resulted in dissolution of X. The correct combination(s) of X and Y respectively is (are):

(Given R = 8.314 J K⁻¹ mol⁻¹, F = 96500 (mol⁻¹)

Options

• Cd and Ni

• Cd and Fe

• Ni and Pb

• Ni and Fe

Answer 1

Cd and Ni, Cd and Fe and Ni and Pb

Explanation:

The metal that dissolves (X) must have a more negative E° than Y.
Fe (–0.44) and Cd (–0.40) have more negative E° than Ni (–0.24) and Pb (–0.13), so Fe and Cd can dissolve when paired with Ni or Pb.

Hence, Fe–Ni, Cd–Ni, and Fe–Pb are correct.