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Question:

To find the standard potential of M³⁺/M electrode, the following cell is constituted: Pt/M/M³⁺(0.001 mol L⁻¹)/Ag⁺(0.01 mol L⁻¹)/Ag. The emf of the cell is found to be 0.421 volt at 298 K. The standard potential of half reaction M³⁺ + 3e⁻ → M at 298 K will be: (Given E°Ag⁺/Ag at 298 K = 0.80 Volt)

0.32 Volt

1.28 Volt

0.66 Volt

0.38 Volt

Solution:

The correct option is A 0.32 Volt
Ecell = E°cell - (0.0592/n)log[M³⁺][Ag⁺]³
0.421 = E°cell - (0.0592/3)log(0.001)(0.01)³
E°cell = 0.48 V
E°cell = E°Ag - E°M
0.48 = 0.80 - E°M
E°M = 0.32 V
The standard potential of half reaction M³⁺ + 3e⁻ → M at 298 K will be 0.32 V.