Electrochemistry: Electrode Potential and Standard Electrode Potential (For CBSE, ICSE, IAS, NET, NRA 2022)

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Electrode Potential

  • Electrode potential is a measure of the tendency of metal atoms to gain or lose electrons when in contact with a solution of its own ions.
  • When a metal strip is immersed in a solution of its salt containing ions , one of the processes as show in in Fig. (a) or (b) can occur.
Electrode Potential

The dissolution process where atoms of metal electrode M may lose some electrons to the electrode and enter the solution as .

(metal is oxidised)

The deposition process where metal cations from the solution may come in contact with the metal strip, gain some electrons and get converted into metal atoms , which get deposited on the surface of metal strip.

(the ion is reduced)

Standard Electrode Potential

  • Electrode Potential is said to be in the standard electrode potential if electrode is in standard state, i.e.. the concentration of the electrolyte is one molar and the temperature is .
  • It is denoted by .
  • If any gas is used to make the electrode, then the pressure of the gas should be 1 bar.

Measurement of Electrode Potential

  • It is not possible to measure single electrode potential because oxidation or reduction cannot take place in isolation.
  • It can be measured with respect to a reference electrode.
  • The electrode used as reference electrode is standard hydrogen electrode (SHE) .

Standard Hydrogen Electrode

  • Standard Hydrogen Electrode (SHE) consists of a container, containing solution kept at .
  • A wire containing Platinum electrode coated with platinum black is immersed in the solution.
  • Pure hydrogen gas is bubbled in the solution at 1bar pressure.
  • The potential of SHE is taken as zero volt at all temperatures.
  • Standard hydrogen electrode may act as anode or cathode depending upon the nature of the other electrode.
  • If its acts as anode, the oxidation reaction taking place is

If it acts as cathode then the reduction half reaction occurring is

Standard Hydrogen Electrode

Determination of Magnitude of Electrode Potential

  • The standard electrode potential of an electrode can be measured by combining it with standard hydrogen electrode.
  • The cell emf is the electrode potential of electrode.

Sign of Electrode Potential

  • The galvanic cell formed by the combination of SHE and electrode under study, the polarity of the electrode is determined with the help of a voltmeter.
  • If the given electrode is found to be positive electrode, its electrode potential is given the positive sign and vice-versa.

Application of Electrochemical Series

Cell Emf and Potential Difference

  • The difference in potential of the two electrodes (or half cells) of a galvanic cell, when measured in the open circuit is called the cell electromotive force or cell emf.
  • When it is measured in a closed circuit with some external load it is called potential difference.

Standard Cell Emf

  • The emf of a cell has a standard value if both its half cells are in their standard states.
  • It is denoted by cell.

Cell Emf and Electrode Potential

The standard cell emf is related to the standard electrode potentials of its anode and cathode.

Cell is related to the electrode potentials of its anode and cathode

Electrochemical Series

Standard potential of a large number of electrodes have been measured and they have been listed in the increasing order of electrode potential in a series called electro chemical series.

Standard Electrode Potential

Standard Electrode Potential

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