Standard Electrode Potentials Aqueous Solutions

Selected standard electrode potentials (V vs. NHE ) in aqueous solution at 25 °C. Data from references (2-A) 

Formal electrode potentials (V vs. aq SCE) at 25 °C for hydrocarbons in solvents. Data from 

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Source Values are compiled from the following sources Bard, A. J. Parsons, R. Jordon, J., eds. Standard Potentials in Aqueous Solutions. Dekker New York, 1985 Milazzo, G. Carol , S. Sharma, V. K. Tables of Standard Electrode Potentials. Wiley London, 1978 Swift, E. H. Butler, E. A. Quantitative Measurements and Chemical Equilibria. Freeman New York, 1972. 

A. J. Bard, R. Parsons and J. Jordan Standard Potentials in Aqueous Solution, Marcel Dekker, New York, 1985, 834 pp. G. Milazzo and S. CarOli, Tables of Standard Electrode Potentials, Wiley, New York, 1978, 421 pp. 

The standard electrode potentials , or the standard chemical potentials /X , may be used to calculate the free energy decrease —AG and the equilibrium constant /T of a corrosion reaction (see Appendix 20.2). Any corrosion reaction in aqueous solution must involve oxidation of the metal and reduction of a species in solution (an electron acceptor) with consequent electron transfer between the two reactants. Thus the corrosion of zinc ( In +zzn = —0-76 V) in a reducing acid of pH = 4 (a = 10 ) may be represented by the reaction ... 

As may be seen from the diagram, silver in highly alkaline solution corrodes only within a narrow region of potential, provided complexants are absent. It is widely employed to handle aqueous solutions of sodium or potassium hydroxides at all concentrations it is also unaffected by fused alkalis, but is rapidly attacked by fused peroxides, which are powerful oxidising agents and result in the formation of the AgO ion Table 6.6 gives the standard electrode potentials of silver systems. 

When the activity of the ion M"+ is equal to unity (approximately true for a 1M solution), the electrode potential E is equal to the standard potential Ee. Some important standard electrode potentials referred to the standard hydrogen electrode at 25 °C (in aqueous solution) are collected in Table 2.5.5... 

The standard electrode potential is a quantitative measure of the readiness of the element to lose electrons. It is therefore a measure of the strength of the element as a reducing agent in aqueous solution the more negative the potential of the element, the more powerful is its action as a reductant. 

STANDARD ELECTRODE POTENTIALS FOR REDUCING IONS IN AQUEOUS SOLUTION All values taken from Ref. 19 unless otherwise indicated. 

Table 5-2 shows the standard chemical free enthalpy for the adsorption of anions observed on several metal electrodes in aqueous solutions of various anions. The magnitude of AGli in the range of 0.1 to 0.7 eV, illustrated in Table 5-2, is of the same order of magnitude as the potential of 0.1 to 1.0 V usually present across the interface of metaUic electrode. On electrodes such as Hg/F and... 

Fig. 5-64. Band edge levels of compound semiconductor electrodes in aqueous solutions at different pH values hydrated redox partides and their standard redox potentials are on the right hand side. [From Gleria-Memming, 1975.]...

Figure 5-64 shows the band edge potential for compound semiconductor electrodes in aqueous solutions, in which the standard redox potentials (the Fermi levels) of some hydrated redox particles are also shown on the right hand side. In studying reaction kinetics of redox electron transfer at semiconductor electrodes, it is important to find the relationship between the band edge level (the band edge potential) and the Fermi level of redox electrons (the redox potential) as is described in Chap. 8. 

The SHE. The H" " H2 couple is the basis of the primary standard around which the whole edifice of electrode potentials rests. We call the H H2 couple, under standard conditions, the standard hydrogen electrode (SHE). More precisely, we say that hydrogen gas at standard pressure, in equilibrium with an aqueous solution of the proton at unity activity at 298 K has a defined value of of 0 at all temperatures. Note that all other standard electrode potentials are temperature-dependent. The SHE is shown schematically in Figure 3.3, while values of Eq r are tabulated in Appendix 3. 

Solubility products can be derived indirectly from standard electrode potentials and other thermochemical data, and directly from tabulated standard Gibbs energies of formation, AfG°, of the ions in aqueous solution [12]. Thus, the use of... 

Aqueous solutions of alkali hydroxides do not attack cadmium. Cadmium replaces elements that are less electropositive in the activity series from their salt solutions. The standard electrode potential ... 

Chlorine reactions may be classified broadly under two types (i) oxidation-reduction and (ii) substitution reactions. The standard electrode potential for Cr — V2CI2 + e in aqueous solution is -1.36 V. Some examples of both types are highlighted briefly below ... 

However, silicon material in an aqueous solution is not a system in equilibrium. It is considered as a mixed system containing two redox couples with standard electrode potentials Ei and Ei separated by a wide interval. Then Eq. (13) must be modified to account for both components ... 

How does the medium affect the nature of reduction of the permanganate in an aqueous solution Compare the values of the standard electrode potentials of the permanganate ion in an acid and neutral media (see Appendix 1, Table 21). 

Table 21, standard electrode potentials E in aqueous solutions AT 298 KiRELATIVE TO THE STANDARD HYDROGEN ELECTRODE... 

The primary reference electrode for aqueous solutions is the standard hydrogen electrode (SHE), expressed by H+(a=l) H2(p=105 Pa) Pt (see 11 in Section 4.1). Its potential is defined as zero at all temperatures. In practical measurements, however, other reference electrodes that are easier to handle are used [24]. Examples of such reference electrodes are shown in Table 5.4, with their potentials against the SHE. All of them are electrodes of the second kind. The saturated calomel electrode (SCE) used to be widely used, but today the saturated silver-silver chloride electrode is the most popular. 

However, it is not an easy matter to relate these scales of E° to the standard electrode potentials in water. This is because of the unknown liquid junction potential that is inevitably introduced when one attempts to calibrate the potential of a reference electrode in a given non-aqueous solution against a common reference electrode, such as the standard hydrogen electrode or saturated calomel electrode in aqueous solution. 

Standard emf Values for the Cell H2/HCl/AgCl, Ag in Various Aqueous Solutions of Organic Solvents at Various Temperatures Temperature Dependence of the Standard Potential of the Silver Chloride Electrode Standard Electrode Potentials of Electrodes of the First Kind Standard Electrode Potentials of Electrodes of the Second Kind Polarographic Half-Wave Potentials (E1/2) of Inorganic Cations Polarographic E1/2 Ranges (in V vs. SCE) for the Reduction of Benzene Derivatives Vapor Pressure of Mercury... 

Table XVI gives recent values of the thermionic work functions for several clean metals and also (for discussion later) the accepted values of the standard electrode potential of the metal in contact with an activity molar aqueous solution of one of its salts, where the concentration is such that the activity coefficient multiplied by the molarity is unity.

The standard electrode potentials for all the rare earths have similar values and are comparable with the redox potentials of alkaline earth metals [144], Thus the lanthanides are strong reducing agents, and form trivalent ions easily. Both europium and samarium can exist in both trivalent and divalent states and the divalent states are not stable in aqueous solutions. Cerium can exist in both tetravalent and trivalent states in solution but Ce(III) is the most stable. 

The common oxidation states of iron are + 2 and + 3. The relative stability of the two oxidation states in acid aqueous solution is defined by the standard electrode potential of + 0.77 V for the Fe3+/Fe2+ couple.1 This potential is such that the hydrated Fe11 cation is thermodynamically unstable with respect to atmospheric oxidation (equation 1). The oxidation is even more favourable in basic solution (equation 2). It is apparent, therefore, that the chemistry of iron, including its... 

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