Electrode potential general table

In general, an electrode with a lower electrode potential in Table 5.1 will reduce the ions of an electrode with a higher electrode potential (Fig. 5.10) or, a high positive standard electrode potential indicates a strong tendency toward reduction, whereas a low negative standard electrode potential indicates a strong tendency toward the... 

Alkanes are functionalised by anodic oxidation in acetonitrile, methanol, acetic acid and more acidic solvents such as trifluoracetic acid and fluorosulphuric acid. Reaction requires very positive electrode potentials (see Table 2.1) and platinum has generally been used as anode materials in laboratory scale experiments. On a larger scale carbon is used as anode material. The first stage in these reactions in-... 

Atmospheric corrosion is electrochemical ia nature and depends on the flow of current between anodic and cathodic areas. The resulting attack is generally localized to particular features of the metallurgical stmcture. Features that contribute to differences ia potential iaclude the iatermetaUic particles and the electrode potentials of the matrix. The electrode potentials of some soHd solutions and iatermetaUic particles are shown ia Table 26. Iron and sUicon impurities ia commercially pure aluminum form iatermetaUic coastitueat particles that are cathodic to alumiaum. Because the oxide film over these coastitueats may be weak, they can promote electrochemical attack of the surrounding aluminum matrix. The superior resistance to corrosion of high purity aluminum is attributed to the small number of these constituents. 

The electron-transfer reactions in Table 1 primarily are metal-centered processes. As a result, the separation between the potentials of successive electrode reactions generally is large. Values of A = K" in Table 1 range from... 

If you study this table carefully, you will note that the first five groups correspond to reactivities and general information with which you are familiar the association of approximate E° values with each group is very helpful. Group 7 contains all the common metals that do not displace H+ s H2 as) from acids. Again, the range and degree of reactivity is related to common experience from a chemist s standpoint it is very helpful to associate an approximate value of the electrode potential with each. 

We also show that, in general, Ox/Red (Mz+/M) couples with high standard electrode potentials are reduced by Ox/Red (Mz+/M) couples with low standard electrode potentials. Or, in other words, low-potential couples reduce high-potential couples (see Table 5.1 and Fig. 5.10). 

A cell to make measurements at equilibrium (potentiometric measurement) needs only two electrodes an indicator and a reference electrode (Fig. 7.3). In general, the indicator electrode is an ion-selective electrode (Section 13.3) and the reference electrode (Table 2.1) is Ag j AgCl or calomel in aqueous solution. The difference in potential between the two electrodes is measured since the reference electrode potential is constant, changes in cell potential are due only to the indicator electrode which responds logarithmically to the activity of the species in solution to which it is sensitive. 

Langmuir,2 in considering the importance of contact potentials for electrolytic cells, pointed out in 1916 that there is a general parallelism between the thermionic work function and the standard electrode potentials. This is shown in Table XVI, where the last column gives the difference between the electrode potential, on the normal hydrogen scale, and the work function. This difference varies much less than the values of either the work function, or the electrode potentials, separately. 

Although a full range of ionization energies is not available throughout the actinide series and thus cannot be used predictively, as for the lanthanides (Table 2.2), electrode potentials are more generally available (Table 9.5) and thus can be so used, as follows ... 

Enols sterically protected at the -carbon have also been investigated. In general, the cyclic voltammetric response exhibits only the already mentioned ECE process, while the reversible benzofuran oxidation is not detected. The pertinent electrode potentials are compiled in Table 2. In the case of the enolato species, the ECE process probably proceeds through separated one-electron oxidations as those of Table 1. 

It is long known that -diketones, which exist as keto-enol tautomers, have a well defined electron transfer ability. In general, they exibit a first, partially chemically reversible, one-electron rednction to the corresponding enolato monoanion (minor amounts of the corresponding dimer are also formed), which in tnrn undergoes either a reduction process or an irreversible oxidation. The electrode potentials of a selection of symmetrically substituted (R = R ) S-diketones are reported in Table 7. 

Electrolytic Oxidation I. Electrode Potential.—A series of stable potentials is difficult to obtain at an anode in the presence of a depolarizer the potential generally rises rapidly from the low value, at which the anode dissolves, to the high value for passivity and oxygen evolution. Since a platinum electrode is nearly always passive, however, it is possible to obtain graded potentials to a limited extent the data quoted in Table LXXXVI were recorded for the oxidation of an acid solution of... 

As stated earlier, the reference electrode in a cell used for electroanalysis is designed so that its potential is independent of the composition of the test solution. There are several general properties that reference electrodes should have in order to be useful in analysis (1) they should be reversible with an electrode potential which is independent of time and reproducible (2) they should have a small temperature coefficient (3) they should be ideally non-polarizable with negligible effects from the flow a small current through the system and (4) they should be easily constructed. The most commonly used reference electrodes are those based on on the mercury calomel system and the silver silver chloride system. The electrolyte most commonly used in these systems is KCl. Relevant parameters for commonly used reference electrodes are given in table 9.4. 

Numerous electrochemical measurements have been carried out with the ruthenium diimin complexes [15], mainly with the aim of comparing electron-transfer processes in the ground and in the excited state, and for the determination of the character of the frontier orbitals. Much less data are known for the cyclometallated analogs. By far the most popular method for the electrochemical measurements is cyclic voltammetry (CV). The measurements are mostly done in nonaqueous solutions (acetonitrile, dimethylfor-mamide, etc.). A general difficulty in such measurements is the reference potential, and the use of an internal standard like, for example, Ru(bpy)2 + is therefore highly recommended. Table 1 contains a compilation of electrode potentials of cyclometallated complexes of the type considered in this review. For comparison, the values of Ru(bpy) + are included in the table. 

It can be seen from Table 3 that the use of different methods to estimate ionization properties of the same monolayers gives somewhat different results. Some conclusions can, however, be reached. In general, acids and bases on the surface become less acidic and less basic, respectively. The difference between surface and bulk pKA values is usually 2-5 pA a units. This conclusion is consistent with the data available for other solid-liquid interfaces. Three examples contradict the above trend (Table 3, lines 12, 13, 14). It can be argued, however, that in the former two cases the electrode potential used could significantly influence surface pK values. Interactions of nitrogen functionalities with the surface, which might have altered the surface pA"a values, also cannot be ruled out307. 

The tendency of a substance to donate or accept elections, and the measure of the electron s availability, is given by its electrode potential. I11 principle, electrode potentials can be measured directly by an electrode and a voltmeter. All chemical elements can transfer electrons and thus change their oxidation states. Table 4.2 shows the standard electrode potentials of the half-reactions of several elements. The general reaction is... 

Table 22.3 shows the standard electrode potentials of the Period 4 transition metals in their -1-2 oxidation state in acid solution. Note that, in general, reducing strength decreases across the series. All the Period 4 transition metals, except copper, are active enough to reduce from aqueous acid to form hydrogen gas. In contrast to the rapid reaction at room temperature of the Group 1A(1) and 2A(2) metals with water, however, the transition metals have an oxide coating that allows rapid reaction only with hot water or steam. 

In general, only the reduction half-reaction potentials are listed in tables, as in Table 9.1. The potential of an oxidation half-reaction is the negative of the value of the reduction half-reaction. Moreover, it is convenient to standardise the concentrations of the components of the cells. If the ceU components are in their standard states, standard electrode potentials, E°, are recorded ... 

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