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
At the anode:
Oxidation ---------------- loss of electrons.
Zn --> Zn2+ + 2e-
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).