The nominal values of the redox standards are rated against the Standard Hydrogen Electrode (SHE), which by definition has a potential of zero. Since normal redox electrodes do not come with a SHE but typically have an built-in silver/silver chloride (Ag/AgCl) electrode, the readings of that redox electrode in these solutions will be approx. 200 mV lower. See the table below.
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Redox Standard +428 mV"ZoBell's Solution", nominal redox value against the Standard Hydrogen Electrode: +428 mV @ 25°C
Redox Standard +675 mV"Light's Solution", nominal redox value against the Standard Hydrogen Electrode: +675 mV @ 25°C
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Potentials of the Pt-Electrode in ZoBell's and Light’s Solution vs. Selected Reference Electrodes:
| Reference Electrode | ZoBell's Solution | Light's Solution | Standard Hydrogen | +428 mV | +675 mV |
|---|---|---|
| Calomel | +183 mV | +430 mV |
| Silver/Silver Chloride in 1 M KCl | +192 mV | +439 mV |
| Silver/Silver Chloride in 4 M KCl | +228 mV | +475 mV |
| Silver/Silver Chloride in saturated KCl | +229 mV | +476 mV |
Potential of ZoBell’s Solution as Function of Temperature:
| Temperature | E |
|---|---|
| 15°C | +450 mV |
| 16°C | +448 mV |
| 17°C | +446 mV |
| 18°C | +443 mV |
| 19°C | +441 mV |
| 20°C | +439 mV |
| 21°C | +437 mV |
| 22°C | +435 mV |
| 23°C | +432 mV |
| 24°C | +430 mV |
| 25°C | +428 mV |
| 26°C | +426 mV |
| 27°C | +424 mV |
| 28°C | +421 mV |
| 29°C | +419 mV |
| 30°C | +417 mV |