Difference between revisions of "Reference Electrode Potentials"
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== The Calomel Electrode == | == The Calomel Electrode == | ||
− | The calomel electrode is usually constructed from a platinum wire inserted into a mixture of calomel (mercurous chloride, Hg<sub>2</sub >Cl<sub>2</sub>) and mercury with an electrolyte solution of KCl or NaCl. The relevant half equation is: | + | The calomel electrode is usually constructed from a platinum wire inserted into a mixture of calomel (mercurous chloride, Hg<sub>2</sub >Cl<sub>2</sub>) and liquid mercury with an electrolyte solution of KCl or NaCl. The relevant half equation is: |
Hg<sub>2</sub >Cl<sub>2</sub> + 2e<sup>–</sup> → 2Hg<sub><i>liq</i></sub> + 2Cl<sup>–</sup> | Hg<sub>2</sub >Cl<sub>2</sub> + 2e<sup>–</sup> → 2Hg<sub><i>liq</i></sub> + 2Cl<sup>–</sup> | ||
Revision as of 13:10, 4 August 2014
The Calomel Electrode
The calomel electrode is usually constructed from a platinum wire inserted into a mixture of calomel (mercurous chloride, Hg2Cl2) and liquid mercury with an electrolyte solution of KCl or NaCl. The relevant half equation is: Hg2Cl2 + 2e– → 2Hgliq + 2Cl–
As this equation implies the electrode potential is dependent on chloride concentration, but independent of hydrogen ion (acid) concentration.
Conditions | vs NHE | vs SCE | LJ | Reference |
---|---|---|---|---|
Hg/Hg2Cl2, KCl (0.1 M) | 0.3337 | 0.0925 | - | 1,3 |
Hg/Hg2Cl2, KCl (0.1 M) | 0.336 | 0.092 | Yes | 2 |
NCE | 0.2801 | 0.0389 | - | 1,3 |
NCE | 0.283 | 0.039 | Yes | 2 |
Hg/Hg2Cl2, KCl (3. 5M) | 0.250 | 0.006 | Yes | 2 |
SCE | 0.2412 | 0 | - | 1,3 |
SCE | 0.244 | 0 | Yes | 2 |
SSCE | 0.2360 | -0.0052 | - | 1 |
Notes
- SCE, saturated calomel electrode: Hg/Hg2Cl2, KCl (sat'd)
- SSCE, saturated salt calomel electrode: Hg/Hg2Cl2, NaCl (sat'd)
- NCE, normal calomel electrode: Hg/Hg2Cl2, KCl (1 M)
- NHE, normal hydrogen electrode
References
(1) "Electrochemical Methods: Fundamentals and Applications", AJ Bard & LR Faulkner, John Wiley & Sons, NY (2000). See the table on inside back cover.
(2) "Electrochemistry for Chemists, Second Edition", DT Sawyer, AJ Sobkowiak, J Roberts, Jr., John Wiley & Sons, NY (1995). See Section 5.2.
(3) "Handbook of Analytical Chemistry", L Meites, ed., McGraw Hill, NY (1963). See Sect 5.