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Calomel Electrode

Reviewed by Raghvendra GopalCheckmark
Last updated: July 19, 2024

What Does Calomel Electrode Mean?

A calomel electrode is a type of reference electrode used in electrochemical measurements to establish a stable reference potential. The calomel electrode is made up of a mercury-mercurous chloride (Hg/Hg2Cl2) electrode in contact with a solution of potassium chloride (KCl). It can be represented as:

Hg|Hg2Cl2KCl (xM) saturated

The electrode reaction is:

Hg2Cl2 + 2e Hg2Cl2 == 2Hg + 2Cl

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Corrosionpedia Explains Calomel Electrode

The calomel electrode is commonly used to establish a reference potential for measuring other electrode's potentials. The calomel electrode's electrode potential is known to be stable and reproducible, which makes it an ideal reference electrode for electrochemical measurements.

In practical applications, the calomel electrode is often used in conjunction with a working electrode to measure the potential difference between two electrodes. This potential difference can be used to calculate the concentration of a substance in solution or to determine the rate of a chemical reaction.

The calomel electrode's potential is defined by the following equation:

Ecalomel = E°calomel + (RT / nF) ln [Hg2Cl2] / [Hg]

Where:

  • "Ecalomel" is the potential of the calomel electrode.
  • "E°calomel" is the standard potential of the calomel electrode.
  • "R" is the gas constant.
  • "T" is the temperature.
  • "n" is the number of electrons transferred in the half-reaction.
  • "F" is Faraday's constant.
  • "[Hg2Cl2]" and "[Hg]" are the concentrations of the mercurous chloride and mercury ions, respectively.

Use of the calomel electrode is not limited to electrochemistry research. It is also used in medical laboratories to measure blood's pH and in environmental monitoring to measure pH and other properties of water samples.

Advantages of using calomel electrodes include:

  • Easy set-up and reproduction.
  • Convenient transportation.
  • Less auxiliary assets required. Calomel electrodes come with a side tube containing a KCI solution, so no separate salt bridge is required.
  • Stable potential. Calomel electrodes' potential does not change appreciably with time nor with slight temperature changes.

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