Class 12 Chemistry Electrochemistry Measurement of electrode potential in a cell

Measurement of electrode potential in a cell

  • The electrode is connected to a standard hydrogen electrode (SHE) to constitute a cell.
  • The electrode forming the negative terminal of the cell is allotted negative value of electrode potential whereas the electrode forming the positive terminal of the cell is allotted a positive value of electrode potential.
  • The potential difference developed between the two terminals is measured using a potentiometer.
  • The direction of the flow of electric current in the external circuit is identified using a galvanometer.
  • This enables us to identify the positive and the negative terminal of the set up as the current flows from positive terminal to negative terminal.
  • This in turn will help us mark the anode and the cathode electrodes due to the fact that the electrons will flow from anode to cathode.

Ecell = Ecathode – Eanode

  • In case of Daniel cell

At the anode:

Oxidation ---------------- loss of electrons.

Zn --> Zn2+ + 2e-

At cathode,

Reduction -------------gain of electrons.

Cu2+ + 2e-  --> Cu

The net reaction of this cell is the sum of two half-cell reactions.
Zn(s) + Cu2+ (aq) --> Zn2+ (aq) + Cu(s)

Emf of the cell = Ecell = Ecathode – Eanode

                                      = 0.34 V – (- 0.76) V = 1.10 V

(Measured Emf of Cu is 0.34 V and that of Zn is 0.76 V).  

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