Reference electrode potential conversion scale

Fig. 6.12 Conversion of an unknown ( ) potential measured with one reference electrode to another reference electrode scale (all values are in millivolts)...

Salt bridges (particularly those that employ saturated KC1) also have been widely used in the conversion of polarographic and other potentials from one reference-electrode scale to another. This conversion is commonly made by direct comparison of the two reference (ref) electrodes in the cell... 

Figure 5 Number line for conversion of electrode potentials among different reference electrode scales.

In this laboratory, you will construct a number line for reference electrode conversions, measure the corrosion potentials of several alloys in a salt water solution, construct a galvanic series with two different reference electrodes, and convert the two galvanic series to the NHE scale to determine if they agree (as they should). This lab will demonstrate some of the concepts discussed in Chapter 2. 

Finally, electrode potential and acidity data were used by Ng et al. to study ligand effects on CpM(PR3)2H2 and TpM(PPh3)2(// -H2)+ (M = Ru, Os) complexes under similar conditions [31] these data are included in Table 3. The Ru-H BDE determined by Ng for CpRu(PPh3)2H2+ (Table 3, entry 19 289 kJ mol" ) is in near perfect agreement with that of Angelici (Table 2, entry 25 286 kJ mol ) but somewhat different from the value derived from Morris data (Table 3, entry 1 303 kJ moF ). The source of the discrepancy might partly be the assumptions and conversions made to align the pXa and electrochemical reference scales of the different solvents used. 

On the laboratory scale, it may be helpful to use three-electrode cells, where the electrochemical potential of the working electrode is set against that of a reference electrode, itself connected to a potentiostat. The purpose of a potentiostat is to fix precisely the reduction (or oxidation) potential necessary for the complete conversion of an organic substrate. At the end of the reaction, the electrochemical current has totally vanished and the concomitant use... 

A survey of the literature, old and recent, reveals that electrochemical experiments are conducted under widely different conditions. Reported electrode potentials for one given compound can vary significantly even under apparently quite similar conditions when published values from different sources are compared. Frequently, this can be caused by erroneous reporting of data or improper conversion of electrode potentials from the scale of one reference electrode to another. Furthermore, the use of different solvents, supporting electrolytes, and physical reference electrodes adds other, physically well understood, reasons why E° data differ, and in many instances should actually differ considerably. It is important at least to understand these effects, and if possible to make reasonable corrections for them. Obviously, there is a definite need to standardize as much as possible the way in which electrode potential data are reported. Errors or discrepancies in E° values will easily lead to significant errors in derived bond energy data. 

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