Standard oxidation potential of the

TABLE 7. pKa (DMSO) of sulfones and standard oxidation potentials of the corresponding carbanions in DMSO... 

In this section, you learned that you can calculate cell potentials by using tables of half-cell potentials. The half-cell potential for a reduction half-reaction is called a reduction potential. The half-cell potential for an oxidation half-reaction is called an oxidation potential. Standard half-cell potentials are written as reduction potentials. The values of standard reduction potentials for half-reactions are relative to the reduction potential of the standard hydrogen electrode. You used standard reduction potentials to calculate standard cell potentials for galvanic cells. You learned two methods of calculating standard cell potentials. One method is to subtract the standard reduction potential of the anode from the standard reduction potential of the cathode. The other method is to add the standard reduction potential of the cathode and the standard oxidation potential of the anode. In the next section, you will learn about a different type of cell, called an electrolytic cell. 

If the standard reduction potential of zinc is -0.76 V, what will be the standard oxidation potentials of the other metals ... 

From measured forward and reverse rate constants of the reaction of a solvated electron with water Baxendale (I) estimated the standard potential for the solvated electron. Use of a more recent rate constant (3) and correction (8) for a certain omitted entropy change yields a value, E° e = + 2.7 volts, for the standard oxidation potential of the solvated electron. To calculate AF0,int for a reaction from a difference of the standard oxidation potentials of the two reactants, E° e — E°, the AF°f must be corrected for the AF0. of about 5 kcal./mole. This correction can be made (8) by taking the effective E° e, E° eff, for a solvated electron to be 2.9 volts. 

To compete effectively with the photophysical processes, the chemical reactions from the highly energetic CT states should be very fast, otherwise the MC states become populated. On the other hand, redox processes may sometimes occur from other than CT excited states. The phenomenon is a consequence of redox potential changes after excitation, which make the entity in any excited state a much stronger oxidant and a much stronger reducer than the ground state complex, eg the standard oxidation potential of the [Fe(bpy)3]2+ complex is 1.05 V in the ground state and... 

It has already been mentioned that it is important to remember in which direction the reaction proceeds in half cells, when calculating the EMF of a cell from the potentials of the half cells, forming that cell, and to draw a correct distinction between the quantities e° and 7t°. Thus e. g. the standard oxidation potential of the element Pt Sn++, Sn++++ has a negative value e° = — 0.15 V. This means that at the electrode in combination with the... 

In this equation sJ> j2, j- represents the standard oxidation potential of the iodine electrode (sJ.tija j- — — 0.535 V) and aj- the activity of iodide ions in the solution. The negative value of this potential means that in combination with a hydrogen electrode a spontaneous reduction process will take place at the iodine electrode during which iodine will pass into the solution in ionic form. 

As already stated, the standard oxidation potential of the calomel electrode related to unity activity of the chloride ion at 25 °C is ea. 11 01101- — —0.268 V. Usually, however, potentials valid directly for various types of calomel electrodes are given (see Table 10). 

The value of for the cell was found to be 0.9834 volt at 25 C, and since the standard (reduction) potential of the right-hand i.e., silver chloride, electrode was recorded above as 0.2224 volt, it follows that the standard (oxidation) potential of the zinc electrode is given by + 0.2224 0.9834 volt, so that n is 0.7610 volt at 25 . 

The standard (oxidation) potential of the oxygen gas electrode is thus — 0.401 volt at 26 C. 

Another important use of standard potentials is for the determination of sdubility products, for these are essentially equilibrium constants ( 39j). If M Al, is a sparingly solvble salt, a knowledge of the standard potentials of the electrodes M, M, A, (s), A - and M, M + permits the solubility product to be evaluated. A simple example is provided by silver chloride Ifor which the standard (oxidation) potential of the Ag, AgCl( ), Cl electrode is known to be — 0.2224 volt at 25 C. The activity of the chloride ion in the standard electrode is unity, and hence the silver ion activity must be equal to the solubility product of silver chloride. The value of Oa may be derived from equation (45.13), utilizing the standard potential of silver thus Eu i — 0.22 volt, E for silver is — 0.799, and z is 1, so that at 25 C,... 

This is the reverse of the standard free energy of formation of the A ion, and consequently the latter is equal to zJFEi where E% is the standard (oxidation) potential of the A, A electrode. ... 

The very exergonic proton transfers in eq.4 are extremely fast. However their rate constants could be determined experimentally if the standard oxidation potential of the arenes (eq.3) could be determined independently under the same experimental conditions (acetonitrile, 0.1 M ionic strength).2 26 jq achieve such measurements we resorted to fast scan cyclic voltammetry. Figure 3 illustrates the merit of on line ohmic drop compensation... 

Similar observations have been made in connection with the Ag, Ag and Fe, Fe " systems as seen above, if all the substances are in their standard states of unit activity, the spontaneous reaction should be the reduction of silver ions to metallic silver by ferrous ions, as is actually the case. The standard oxidation potentials of the two systems are not very different, although that of the Fe ", Fe system is the higher. 

---