calomel electrode
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Introduction
The calomel electrode consists of mercury covered by a layer of calomel (Hg2Cl2), which is in contact with an electrolyte solution containing Cl-. The electrode process is:
1/2 Hg2Cl2 (solid) + e- <---> Hg(metal) + Cl-
Since aHg & aHg2Cl2 are both unity (present as pure substance), the electrode potential reduces to:
E = E* - N x log aCl-
This shows that the calomel electrode also functions as a chloride electrode & that its potential varies with the Cl- activity. The Cl- activity is generally maintained constant, either as saturated KCl or at a concentration of 3.5 (or 4.0) M. Calomel electrodes are frequently employed for pH measurement as reference electrodes together with glass electrodes.
More general terms
References
- ↑ Tietz Textbook of Clinical Chemistry, 2nd ed. Burtis CA & Ashwood ER (eds), WB Saunders Co, Philadelphia PA, 1993, pg 165