Nickel standard reduction potentials

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 ... 

A FIGURE 20.26 illustrates an electrolytic cell for electroplating nickel onto a piece of steel. The anode is a strip of nickel metal, and the cathode is the steel. The electrodes are immersed in a solution of NiS04(external voltage is applied, reduction occurs at the cathode. The standard reduction potential of Ni (E°ei 0.28 V) is less negative than that of H2O (E°ed = —0.83 V), so Ni is preferentially reduced, depositing a layer of nickel metal on the steel cathode. 

No. Steel is mostly iron whose standard reduction potential is more negative than that of nickel, so it would still be the iron that is oxidized if it is coupled with nickel. 

Since the standard reduction potential for hydrogen gas evolution is more positive than that of nickel deposition, it is thermodynamically favored. To reduce the likelihood of hydrogen evolution, the concentration of hydrogen ion is lowered. Thus, an electrolyte pH of 3.0-3.5 is needed in sulfate electrolytes to effectively deposit nickel. 

FE An electrochemical cell is composed of pure O nickel and pure iron electrodes immersed in solutions of their divalent ions. If the concentrations of Ni and Fe ions are 0.002 M and 0.40 M, respectively, what voltage is generated at 25°C (The respective standard reduction potentials for Ni and Fe are -0.250 V and -0.440 V.)... 

In Table II the reduction potentials of a variety of nickel(III) complexes are reported. The values have been corrected as well as is possible for standard conditions and it is revealing that the potentials, particularly of complexes which have a strong square-planar ligand, show marked variations depending on the donor ability of the solvent and coordinating anions. This has itself evolved into a structural probe (108, 117) but clearly it makes comparisons difficult and overinterpretation somewhat dangerous. 

The midpoint reduction potentials of the various EPR-detectable nickel species in hydrogenase are all less than 0 mV versus the standard hydrogen electrode (Table II). This is in contrast to synthetic inorganic complexes with amino acids 44), in which the oxidation of Ni(II) to Ni(III) occurs at much higher potentials (0.8-1.2 mV) and is accompanied by reorganization of the complex 45). This requires some explanation in view of the interpretation of the Ni-A EPR signal as Ni(III)(7). 

The standard electrode potential for the reduction of Ni- to Ni is — 0.25V. Would the potential of a nickel electrode immersed in a 1.00 M NaOH solution saturated with Ni(OH)2 be more negative than -/Ni or less Explain. 

We can confirm this by calculating the standard electrode potential for manganese acting as the anode (oxidation) and nickel acting as the cathode (reduction). 

Because of lithium s low density and high standard potential difference (good oxidation reduction characteristics), cells using lithium at the anode have a very high energy density relative to lead, nickel and even zinc. Its high cost limits use to the more sophisticated and expensive electronic equipment. 

The reduction is thermodynamically favored, because the standard potential of the couple Cu2+/Cu is positive (E° = +0.34 V). Metals with negative standard potentials, such as zinc (E° = —0.76 V) and nickel (E° = —0.23 V), cannot be extracted hydrometallurgically. 

Since the half-wave potential is characteristic of the particular reaction that is occurring at that potential, it is possible to identify the species involved. A simple case is shown in Figure 3 where a mixture of metal ions was analyzed. The two reduction waves for copper occur at -0.1 and -0.35 V, cadmium at -0.69, nickel at -1.10 and zinc at -1.35 V. This illustrates an analysis that may identify the species qualitatively and, by using a standard addition method, can also determine the ions quantitatively. 

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