Standard reduction potentials determination

C19-0026. Using standard reduction potentials, determine A G ° and. eq at 25 °C for each of the following reactions ... 

The standard reduction potentials determined in aqueous solution give hierarchies slightly different from the antioxidant hierarchy established in DMF. For the potential determined by pulse radiolysis the ordering according to tendency of regeneration is (Jovanovic et al, 1994) ... 

Using the table of standard reduction potentials, determine if either PhO or PhOg is stable in a water solution at pH 9. 

Zinc is another common impurity in copper. Using standard reduction potentials, determine whether zinc will accumulate in the anode sludge or in the electrol) c solution during the electrorefining of copper. 

Standard, reduction potentials are determined by measuring the voltages generated in reaction half-cells (Figure 21.2). A half-cell consists of a solution containing 1 M concentrations of both the oxidized and reduced forms of the substance whose reduction potential is being measured, and a simple electrode. 

It is clear from what has already been stated that standard reduction potentials may be employed to determine whether redox reactions are sufficiently complete... 

Tabulated standard reduction potentials allow us to determine the potential of any cell under standard conditions. This net standard cell potential is obtained by subtracting the more negative standard reduction potential from the more positive standard reduction potential, giving a positive overall potential. 

C19-0020. Use standard reduction potentials to determine the net reaction and standard cell potential for cells of two compartments, each containing a 1.00 M solution of the indicated cation in contact with an... 

Use tabulated standard reduction potentials to determine for the following redox reaction ... 

This is a quantitative calculation, so it is appropriate to use the seven-step problem-solving strategy. We are asked to determine an equilibrium constant from standard reduction potentials. Visualizing the problem involves breaking the redox reaction into its two half-reactions ... 

C19-0134. Use standard reduction potentials from Table 19-1 and Appendix F to determine. sp for as many metal hydroxides as the table allows. Compare your values with those in Appendix E. If there are. sp values for hydroxides in Appendix E that cannot be calculated from standard reduction potentials in Appendix F, use the. STjp values to calculate the appropriate standard reduction potentials. 

The electron transfer mechanism for antioxidant activity corresponding to eq. 16.5 makes the standard reduction potentials of interest for evaluation of antioxidative activity. The standard reduction potential of the phenoxyl radical of several flavonoids has been determined and forms the basis for correlation of rate of electron transfer for various oxidants from the flavonoid (Jovanovic etal., 1997 Jorgensen and Skibsted, 1998). The standard reduction potentials have also been used to establish antioxidant hierarchies. 

For aqueous solutions, ascorbate can be included in the hierarchy, while a-tocopherol has to be replaced by its water-soluble analogue trolox, which is often assumed to have the same standard reduction potential. The ordering of the antioxidants based on the two different determinations of E in water is rather similar, and it should be noted that ascorbate is the antioxidant which will regenerate the other antioxidants, with the ascorbate itself ending up being oxidised. In contrast to what was observed for DMF, the ordering in water predicts that quercetin could regenerate a-tocopherol from its oxidised form. 

They are the basis of many products and processes, from batteries to photosynthesis and respiration. You know redox reactions involve an oxidation half-reaction in which electrons are lost and a reduction half-reaction in which electrons are gained. In order to use the chemistry of redox reactions, we need to know about the tendency of the ions involved in the half-reactions to gain electrons. This tendency is called the reduction potential. Tables of standard reduction potentials exist that provide quantitative information on electron movement in redox half-reactions. In this lab, you will use reduction potentials combined with gravimetric analysis to determine oxidation numbers of the involved substances. 

The table of standard reduction potentials assists in the determination as to whether species can react with each other, or not. This can be substantiated by considering the reaction of hydrogen with two metals, copper and zinc. In order to determine whether or not a reaction takes place spontaneously under standard conditions, one calculates the standard potential using hydrogen ions and the metal as reactants. 

The more the two half-reactions are separated in the table, the greater is the tendency for the net reaction to occur. This tendency for an overall redox reaction to occur, whether by direct contact or in an electrochemical cell, is determined from the standard reduction potentials, E° values, of the half-reactions involved, and the value of this potential are indications of the tendency of the overall redox reaction to occur. We will now present a scheme for determining this potential, which is symbolized E"d. ... 

Using the above information, determine the standard reduction potential for the following reaction ... 

In aqueous solution, thorium exists as Th(IV), and no definitive data have been presented for the presence of lower-valent thorium ions in this medium. The standard potential for the Th(IV)/Th(0) couple has not been determined from experimental electrochemical data. The values presented thus far for the standard reduction potential have been calculated from thermodynamic data or estimated from spectroscopic measurements. The standard potential for the four-electron reduction of Th(IV) ions has been estimated as —1.9 V in two separate references 12. The reduction of Th(OH)4 to Th metal was estimated at —2.48 V in the same two publications. Nugent et al. calculated the standard potential for the oxidation ofTh(III) to Th(IV) as +3.7 V versus SHE, while Miles provides a value of +2.4 V [13]. The standard potential measurements from studies in molten-salt media have been the subject of some controversy. The interested reader is encouraged to look at the summary from Martinot [10] and the original references for additional information [14]. 

To determine the E° of different cell arrangements, chemists use what are called standard reduction potentials for halfcells. A standard reduction potential is the electrical potential under standard conditions of a cell compared to the standard hydrogen electrode. The standard hydrogen electrode is a special half-cell that has been chosen as a reference to measure electrical potential. Just as sea level is a logical elevation for measuring gravitational potential,... 

One more example demonstrates how to use standard reduction potentials to determine the standard potential of a cell. Let s say you wanted to construct a cell using silver and zinc. This cell resembles the Daniell cell of the previous example except that a silver electrode is substituted for the copper electrode and a silver nitrate solution is used in place of copper sulfate. From Table 14.2, it is determined that when silver and copper interact silver is reduced and copper oxidized. The two relevant reactions are... 

Q I rom the data given in fable 6.X. comment on the role of the ulomi/ulion enthalpies in determining the trend in the observed standard reduction potentials for the Na. Mg and Al couples. 

When two conjugate redox pairs are together in solution, electron transfer from the electron donor of one pair to the electron acceptor of the other may proceed spontaneously. The tendency for such a reaction depends on the relative affinity of the electron acceptor of each redox pair for electrons. The standard reduction potential, E°, a measure (in volts) of this affinity, can be determined in an experiment such as that described in Figure 13-14. Electrochemists have chosen as a standard of reference the half-reaction... 

First, the standard reduction potentials of the individual electron carriers have been determined experimentally (Table 19-2). We would expect the carriers to function in order of increasing reduction potential, because electrons tend to flow spontaneously from carriers of lower E ° to carriers of higher E °. The order of carriers deduced by this method is NADH - ... 

Q —> cytochrome b —> cytochrome c1 —> cytochrome c —> cytochrome a —> cytochrome a3 —> 02. Note, however, that the order of standard reduction potentials is not necessarily the same as the order of actual reduction potentials under cellular conditions, which depend on the concentration of reduced and oxidized forms (p. 510). A second method for determining the sequence... 

Mechanism 1 is a simple rate-determining outer-sphere electron transfer between hydroxide and the tris(diimine)metal(III) reactant. This mechanism is, however, not very plausible for the reactants in Table II, because, first, the enthalpy of activation is significantly less than the enthalpy of reaction (6). Second, the standard reduction potential for Eq. (5)... 

Calculate E° for the reaction from standard reduction potentials, as in Worked Example 18.5. Then use the equation log K = nE°/0.0592 V to determine the equilibrium constant. 

The numerical value of an electrode potential depends on the nature of the particular chemicals, the temperature, and on the concentrations of the various members of the couple. For the purposes of reference, half-cell potentials are taken at the standard states of all chemicals. Standard state is defined as 1 atm pressure of each gas (the difference between 1 bar and 1 atm is insignificant for the purposes of this chapter), the pure substance of each liquid or solid, and 1 molar concentrations for every nongaseous solute appearing in the balanced half-cell reaction. Reference potentials determined with these parameters are called standard electrode potentials and, since they are represented as reduction reactions (Table 19-1), they are more often than not referred to as standard reduction potentials (E°). E° is also used to represent the standard potential, calculated from the standard reduction potentials, for the whole cell. Some values in Table 19-1 may not be in complete agreement with some sources, but are used for the calculations in this book. 

Standard [reduction] potentials for hundreds of electrodes have been determined (mostly in the period 1925-45, during which time they were referred to as oxidation potentials ) and are usually tabulated in order of increasing tendency to accept electrons. This ordering is also known as the electromotive series of the elements. As can be seen in the abbreviated version in Table 1, sodium is the most active of the metallic elements in the sense that its oxidation product Na+ shows the smallest tendency (as indicated by the highly negative voltage) to undergo reduction. 

Whether one metal will replace another metal from a compound is determined by the reduction potential of the metal, found on a table of standard reduction potentials (like the one available to you on the AP test). If the metallic element is higher on the chart than the cation, it will replace it. If it is not higher on the chart, no reaction will occur. 

Answer The better oxidizing agent will be the substance that is the easiest to reduce (has more positive reduction potential). To determine the reduction potential of these two species, you need to locate the half-reaction that shows each as the reactant. Chapter 1 has a table of standard reduction potentials that you can use for this question. The values for Cl2 and Fe3+ are ... 

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