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Question

The standard electrode potential of two half cells is given below-

Ni2++2e-Ni ; E10=-0.25V

Zn2++2e-Zn ; E20=-0.77V

The voltage cell formed by combining the two half cells would be:


A

+0.52V

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B

-0.52V

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C

+1.02V

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D

-1.02V

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Solution

The correct option is A

+0.52V


Explanation of Correct option:

(A) +0.52V

Standard Electrode Potential:

  • A measurement of the potential for equilibrium is the standard electrode potential.
  • The electrode's potential is the difference in potential between the electrode and the electrolyte.
  • The electrode potential is referred to as the standard electrode potential when unity represents the concentrations of all the species involved in a semi-cell.

Given Reactions:

Ni2++2e-Ni ; E10=-0.25V

Zn2++2e-Zn ; E20=-0.77V

  • Hence for oxidation to take place, we reverse both the reactions,

NiNi2++2e-; EO.P.0=+0.25V

ZnZn2++2e- ; EO.P.0=+0.77V

  • The sign of electrode potential also reverses.
  • Hence the oxidation potential of Zinc is more so we will take it as Anode and Nickel as Cathode.
  • The reaction can be represented as,

Zn|Zn2+Anode||Ni2+|NiCathode

  • Hence there will be oxidation on the anode and reduction at the cathode.
  • Now the standard electrode potential of the cell is written as,

Ecell0=EZn|Zn2+0+ENi2+|Ni0

=+0.77V-0.25V=+0.52V

Explanation of incorrect option:

(B) -0.52V

  • If the oxidation potential of Zinc would have been negative i.e. E20=-0.77V, and that of Nickel is also negative i.e. EO.P.0=-0.25V then standard electrode potential of the cell will be -0.52V.

(C) +1.02V

  • If the oxidation potential of Nickel would have been negative i.e. E10=-0.25V, then standard electrode potential of the cell will be +1.02V.

(D) -1.02V

  • If the oxidation potential of Zinc would have been negative i.e. E10=-0.77V, and that of Nickel is positive i.e. EO.P.0=+0.25V then standard electrode potential of the cell will be -1.02V.

Hence correct option is (A)


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