Reduction potentials cadmium

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... 

Other Substrates Deposition of cadmium was also studied on Bi, Sn and Pb [303], Ni [304], reticulated vitreous carbon [305], Ti [306], and indium tin oxide [307]. UPD of Cd on tellurium results in CdTe formation [270, 308]. Electrodes coated with conducting polymers were also used to deposit cadmium electrochemi-cally. In the case of polyaniline, the metal reduction potential corresponds to the neutral (nonconducting) state of the polymer, therefore cadmium was found to deposit on the substrate-glassy carbon electrode surface, in the open pores of the polymer film [309, 310]. 

Of the Group 12 elements, zinc, cadmium and mercury, only Hg has a water-stable -I-1 state, and all three elements have + 2 states that are water-stable. Their reduction potentials are summarized in the Latimer diagram ... 

The iron-nickel oxide alkaline battery system has many features in common with the nickel-cadmium system discussed above. It was first developed by Edison in the USA at the turn of the century and was patented in the same year as Jungner s first nickel-cadmium US patent, 1901. Iron can be regarded as a favourable active battery material because of its low cost, high theoretical specific capacity (twice that of cadmium) and non-toxic, pollution-free characteristics. However, because its reduction potential is below that of hydrogen, and since hydrogen overvoltage is low on iron, charge retention is poor and efficiency is low. 

Similarly at the cadmium electrode oxidation will take place at the oxidation potential s° = 0.402 V, when combining with the copper electrode, which due to its nobler nature acts in this system as a positive electrode with a reduction potential v ° — 0.345 V ... 

Electrowinning of metals in aqueous solutions is applicable to those metals that possess high electrochemical reduction potentials, such as silver, copper, cadmium, and zinc. Magnesium, aluminum, and sodium, like other reactive metals, are electro-produced from molten salt baths, such as NaCl/CaCh mixture at ca. 600 °C for sodium and MgCl2/NaCl/CaCl2 eutectic mixture at ca. 750 °C for magnesium. 

I". Cadmium sulfide (CdS) is used in some semiconductor applications. Calculate the value of the solubility product (Ksp) for CdS given the following standard reduction potentials ... 

Unfortunately, the copper product requires extensive refining before being marketable. Moreover, scrap iron cannot displace zinc, cadmium, or many other trace contaminants from solution. Zinc is more versatile than scrap iron, having a lower reduction potential. However, although zinc is used extensively in hydrometallurgical processes to cement copper, nickel, and cobalt from zinc leach solutions before electrolysis " and to recover gold and silver in the Merrill-Crowe process. the Zn + ions introduced into solution would be unacceptable for environmental applications, even if the process were economically attractive. 

Zinc and cadmium dissolve in dilute acid to give their -I- 2 ions, but mercury does not dissolve, as indicated by the two positive reduction potentials. Mercury forms the diatomic Hg2 ion, in which the Hg-Hg bond length is 251 pm, consistent with it being a single ct bond formed from the overlap of the two 6s atomic orbitals. The reason for the relatively greater stability of the 6s electrons of Hg is relativistic stabilization which causes the first two ionization energies (1010 and 1810 kJ mol ) to be considerably greater than those of Zn (908 and 1730 kJ mol ) and Cd (866 and 1630 kJ mol ). 

Differences in the reduction potentials for copper, bismuth, lead and cadmium with a dropping mercury electrode has been seen In Figure 12.. Similar differences exist If a platinum electrode Is used providing a suitable depolarizing agent Is employed to prevent excess polarization at the anode. Hydrazine hydrochloride or hydroxylamlne hydrochloride are the usual depolarizers (l4). 

Copper-coated cadmium filings or fine granules are very suitable for the heterogeneous reduction, but in a neutral or weakly alkaline medium the cadmium ions formed during the reduction of the nitrate react with hydroxyl ions and form a precipitate. Furthermore, the reduction potential needed for the reduction of nitrate to nitrite depends on the hydrogen ion activity according to the Nemst equation ... 

Consider a voltaic ceU constructed from a cadmium electrode and a silver electrode having the following reduction half-reactions and corresponding standard electrode potentials (reduction potentials) ... 

Calculation of Cell emfs Using Standard Reduction Potentials Note that in the case of the cadmium-silver cell above the emf of the cell equals the standard electrode potential of the cathode minus the standard electrode potential of the anode. So, alternatively, you can calculate any cell emf using the equation... 

---