Element standard reduction potential

Although it is only slowly oxidized in moist air at ambient temperature, cadmium forms a fume of brown-colored cadmium oxide [1306-19-0] CdO, when heated in air. Other elements which react readily with cadmium metal upon heating include the halogens, phosphoms, selenium, sulfur, and tellurium. The standard reduction potential for the reaction... 

Consistent with this, even KI3 is rapidly decolorized in alkaline solution. The example is a salu-tory reminder of the influence of pH, solubility, and complex formation on the standard reduction potentials of many elements. 

Tlic power of these various concepts in codifying and rationalizing the redox chemistry of the clcineiUs is ilhislraled for Ihe case of nitrogen in tbe present section Standard reduction potentials and plots of volt equivalents against oxidation state fur odicr elements are presented in later chapters... 

The standard reduction potentials of the elements in acid and alkaline solutions are summarized in the schemes below.It is... 

If the free element is less active than the corresponding element in the compound, no reaction will take place. A short list of metals in order of their reactivities and an even shorter list of nonmetals are presented in Table 7-1. The metals in the list range from very active to very stable the nonmetals listed range from very active to fairly active. A more comprehensive list, a table of standard reduction potentials, is presented in general chemistry textbooks. 

In Table 7-1 the relative tendencies of certain elements to react were listed qualitatively. We can give a quantitative measure of relative tendency to react, called standard reduction potential, as shown in Table 14-2. In this table, the standard half-cell potential for each half-reaction, as a reduction, is tabulated in order with the highest potential first. If we turn these half-reactions around, we change the signs of the potentials and we get oxidation potentials. We thus have half-reactions including both elementary metals and elementary nonmetals in the same table, as well as many half-reactions that do... 

FIGURE 12.3 Schematic depicting the electron flow in an enzyme-catalyzed mediated electron transfer oxidation of substrate. The relative magnitudes of the standard reduction potentials of each element for efficient mediation are shown beneath the scheme. 

In an electroplating process, once the concentration of the element of interest, e.g. Cu2+, is sufficiently low, the impurity metal cations will start plating out of solution onto the object (cathode - source of electrons). The order of plating depends both on the reduction potentials of the metals and their concentrations. If we assume that the impurity concentrations are the same in the solution, then the most easily reduced species will be the first one to plate out. This is the metal with the most positive standard reduction potential. Of the metals given in the problem, the order in which the metals will plate out is ... 

The standard reduction potential for Be2+ is the least negative of the elements in the group and by the same token beryllium is the least electropositive and has the greatest tendency to form covalent bonds. The bulk metal is relatively inert at room temperature and is not attacked by air or water at high temperatures. Beryllium powder is somewhat more reactive. The metal is passivated by cold concentrated nitric acid but dissolves in both dilute acid and alkaline solutions with the evolution of dihydrogen. The metal reacts with halogens at 600°C to form the corresponding dihalides. 

Transition metals tend to have higher melting points than representative metals. Because they are metals, transition elements have relatively low ionization energies. Ions of transition metals often are colored in aqueous solution. Because they are metals and thus readily form cations, they have negative standard reduction potentials. Their compounds often have unpaired electrons because of the diversity of -electron configurations, and thus, they often are paramagnetic. Consequently, the correct answers are (c) and (e). 

Latimer diagrams were invented by W. M. Latimer and consist of lines of text of the various oxidation states of an element arranged in descending order from left to right, with the appropriate standard reduction potentials (in volts) placed between each pair of states. The diagram for chromium in acid solution is written as ... 

From the Latimer diagram for the element M. calculate the standard reduction potential for the M M reduction, and... 

From the values of the standard reduction potentials of the follow ing couples, comment on the stability of the oxidized forms and the reduced forms of the elements ... 

Table 6.4 The standard reduction potentials for the metallic elements of Groups 1 and 2 at pH = 0 ...

Table 6.7 Standard reduction potentials for the Group 13 elements at pH = 0 and pH = 14...

The standard reduction potentials for the elements of Group 15 at pH values of 0 and 14, respectively, are given in Tables 6.10 and 6.11, which include only the main and well-characterized ions and some molecular species. 

The standard reduction potentials for the main species formed by the Group 17 elements in aqueous solution are given in Tables 6.16 and 6.17, for pH values 0 and 14, respectively. Irrespective of the pH of the solution, the halogen elements range from the extremely powerful F2 (which has the potential to oxidize water to dioxygen), through the powerful oxidants Cl2 and Br2, to 12, which is a relatively weak oxidant. 

Table 7.14 Data (all in kJ mol 1) (or Ca and the first-row transition elements, and the calculated standard reduction potentials for the reduction of M2 to the element, M...

The elements of the Group, including La and Lu, are powerful reducing agents, and their 4- 3/0 standard reduction potentials in I mol dm 3 acid solution are summarized by the Latimer diagrams shown in the margin. 

Only the + 2 state of cobalt has thermodynamic stability in acid solution. The instability of Co3+ is referred to in Section 5.3. Only the + 3 states of Rh and Ir are stable in acid solution their +3/0 standard reduction potentials are quite positive, consistent with their nobility . In alkaline solutions the + 2 and + 3 states of the elements exist as insoluble hydroxides. 

Of the Group 10 elements, nickel, palladium and platinum, only the +2 states of Ni and Pd are well characterized in aqueous acid solutions. Their + 2/0 standard reduction potentials in acid solution are given in the Latimer diagram ... 

It allows an estimate to be made of the standard reduction potentials of the lanthanide elements. 

The calculated and experimental values of the + 3/0 standard reduction potentials for the lanthanide elements are given in Table 8.5. 

From data given in the text, compare the standard reduction potentials of the l. 1 2 and 3 oxidation stales of the elements ("s. Bn and Lit. respectively, and their zero oxidation states. Identify the factors l ha I are responsible for the observed trend in the values of the standard potentials. 

The table gives the required data (kJ mol for enthalpies and ionization energies) and the calculated values of the standard reduction potentials for the three elements. 

The nature of ions in solution is described in some detail and enthalpies and entropies of hydration of many ions are defined and recalculated from the best data available. These values are used to provide an understanding of the periodicities of standard reduction potentials. Standard reduction potential data for all of the elements, group-bygroup, covering the s-and p-, d- and/- blocks of the Periodic Table is also included. Major sections are devoted to the acid/base behaviour and the solubilities of inorganic compounds in water. 

Appendix H contains standard reduction potentials arranged alphabetically by element. If the half-reactions were arranged according to descending value of E° (as in Table 14-1),... 

A Latimer diagram displays standard reduction potentials E°, connecting various oxidation states of an element.11 For example, in acid solution, the following standard reduction potentials are observed ... 

In the past the electrostatic convention has often been called the European convention and the thermodynamic convention popularized by Luitmer (The Oxidation Potentials of the Elements and Their Values in Aqueous Solution Prenlicc-HBlI Englewood Cliffs. NJ, (952) the American convention. In an effort to reduce confusion, the IUPAC adopted the "Stockholm convention" in which electrode potentials refer to the electrostatic potential and end s refer to the thermodynamic quantity. Furthermore, the recommendation is that standard reduction potentials be listed as electrode potentials" to avoid the possibility of confusion over signs. 

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