Copper standard electrode potential

When metals are arranged in the order of their standard electrode potentials, the so-called electrochemical series of the metals is obtained. The greater the negative value of the potential, the greater is the tendency of the metal to pass into the ionic state. A metal will normally displace any other metal below it in the series from solutions of its salts. Thus magnesium, aluminium, zinc, or iron will displace copper from solutions of its salts lead will displace copper, mercury, or silver copper will displace silver. 

Therefore, criteria in the selection of an electrode reaction for mass-transfer studies are (1) sufficient difference between the standard electrode potential of the reaction that serves as a source or sink for mass transport and that of the succeeding reaction (e.g., hydrogen evolution following copper deposition in acidified solution), and (2) a sufficiently low surface overpotential and rate of increase of surface overpotential with current density, so that, as the current is increased, the potential will not reach the level required by the succeeding electrode process (e.g., H2 evolution) before the development of the limiting-current plateau is complete. 

We now return to the case of codeposition of metals whose standard electrode potentials are wide apart. As stated, the deposition potentials [Eq. (11.2)] are brought together by complexing the more noble metal ions, as illustrated below for the case of the codeposition of copper and zinc as brass. 

The complete zinc-copper cell has a total potential of 1.10 volts (the sum of 0.76v and 0.34v). Notice that the sign of the potential of the zinc anode is the reverse of the sign given in the chart of standard electrode potentials (see Table 12-4) because the reaction at the anode is oxidation. 

In the chart of standard electrode potentials (Table 12-1), reactions are arranged in order of their tendency to occur. Reactions with a positive EMF occur more readily than those with a negative EMF. The zinc-copper cell has an overall EMF of + 1.10 volts, so the solution of zinc and deposition of copper can proceed. 

The chemistry of fluorine is dominated by its electronegativity, which is the highest of all elements. The colorless gas F2 has an estimated standard electrode potential E° (Chapter 15) of +2.85 V for reduction to F (cf. + 1.36 V for Cl2 to Cl-), and thus F2 immediately oxidizes water to oxygen (E° = +1.23 V), and 2% aqueous NaOH to the gas F20. Obviously, F2 cannot be made by electrolysis of aqueous NaF. The usual preparation involves electrolysis of HF-KF melts in a Monel (Cu-Ni alloy) or copper apparatus. 

The driving force for copper deposition (reaction 16.2) is much greater than for zinc precipitation (reaction 16.1), as the corresponding standard electrode potentials of +0.340 and -0.763 V indicate. Consequently, if the copper and zinc strips are placed in the same aqueous medium and are in electrical contact with each other as in Fig. 16.1, reaction 16.2 will proceed in the direction left to right by driving reaction 16.1 in the sense right to left. The zinc will therefore dissolve while the copper ions in the aqueous phase are redeposited. 

Solvent displacement, and isotherms. 954. 955 Solvent excess entropy at the interface, 912 Solvent interactions, 923, 964 Soriaga, M., 1103, 1146 Specifically adsorbed ions, 886 Spectrometer, 797 Spikes, electrodeposition. 1336 Spillover electrons, of metal, 889 Spiral growth, electrodeposition, 1316, 1324, 1326, 1324,1328 s-polarized light, 802 Srinivasan, S 1439,1494 Standard electrode potential American convention, 1354 convention, 1351 rUPAC convention, 1355 prediction of reactions, 1359 the zinc-minus and copper-plus convention, 1352... 

Once this standard electrode potential is known by means of experimental measurements, the Nemst equation permits a calculation of what the electrode potential will be when the solution has any other cIq + titan the value of unity used in the standard potential. For example, the electrode potential of a copper electrode on the standard hydrogen scale immersed in aCu2+ solution of Oq =2 X 10-2 would be (Fig. 7.16)... 

In consulting tables of standard electrode potentials (see Table 7.23), it is neces-saiy to be aware of an (unfortunate) difference in conventions for the sign of the E° values. Consider, e.g., the E° values for zinc electrodes dipped in Zn2+ solutions of unit activity and for copper electrodes dipped in Cu2+ solutions of unit activity. Tables... 

Thus, the IUPAC decision supports the zinc-minus-copper-plus table of standard electrode potentials. The first thing to do, therefore, when consulting a table of standard electrode potentials is to examine the E° values of the zinc and copper electrodes. If the values are -0.76 and +0.34 V, respectively, the table can be used. If, however, the values are +0.76 and -0.34 V, the convention contravenes the IUPAC decision. To use such a table, one can retain all the magnitudes of the E° values, but change all the signs of the E° values the table will then be in accord with the international convention (Table 7.23). 

The values of the standard electrode potentials of copper (Cu+ + e- -> Cu, 0.522 V) and zinc (Zn2+ + 2e - Zn, —0.76 V) make it appear unlikely that the metals could be codeposited as the alloy brass. However, if, for example, solutions which are 0.025 M in [Zn(CN)4]2 and 0.05 M in [Cu(CN)3]2 are mixed, simple calculation can show that the static electrode potentials of the two ions have values which approach each other more closely and codeposition becomes much more probable. This can be understood with the help of equation (5) and the knowledge that the dissociation constants of [Zn(CN)4]2 (1.3 x 10-17) and [Cu(CN)3]- (5.6 x 10-28) will greatly modify the activity term. 

The standard electrode potential can be obtained by connecting a hydrogen electrode system to a copper electrode system through a U-bridge and a voltmeter, as shown in Figure 1.4. In this system copper is the cathode since reduction occurs. 

III.10 COPPER, Cu (Ar 63-54) Copper is a light-red metal, which is soft, malleable, and ductile. It melts at 1038°C. Because of its positive standard electrode potential (+0- 34 V for the Cu/Cu2+ couple) it is insoluble in hydrochloric acid and in dilute sulphuric acid, although in the presence of oxygen some dissolution might take place. Medium-concentrated nitric acid (8m) dissolves copper readily ... 

The standard electrode potentials are far more anodic than that of one-electron transfer process, -0.284 V (SHE) and the visible-light photocatalytic activity of platinum-loaded tungsten(VI) oxide could be interpreted by enhanced multiple-electron transfer process by deposited platimun (45), since it is well known that platinum and the other noble metals catalyze such multiple-electron transfer processes. Similar phenomena, cocatalyst promoted visible-light photocatalytic activity, have been reported with palladium 46) and copper oxide (47). Thus, change of reaction process seems beneficial to realize visible-light photocatalytic activity. 

If Ezn,zn and Ecu,cu represent the standard electrode potentials on the hydrogen scale of the zinc and copper electrodes, as recorded in Table XLIX, then Eza.zn is actually the e.m.f. of the cell... 

The standard electrode potential, , and pe A simple redox reaction in which dissolved copper-II ion is converted to elemental copper and elemental zinc is converted to the corresponding zinc-II cation is... 

In the equilibrium state, the anodic and cathodic partial reactions of an electrochemical reaction have equal rates. The system is in a dynamic equilibrium state, and no net reaction occurs. For example, when a copper sheet is immersed in copper sulfate solution, in the equilibrium state the anodic dissolution rate of copper from sheet to solution equals the cathodic deposition rate from the solution to the surface of the sheet. Theoretically, one can calculate the equilibrium state of an electrochemical reaction from thermodynamic values. This is the standard electrode potential, E°, or equilibrium potential of the electrochemical reaction. The standard electrode potential corresponds to a determined standard state of 0.1 MPa, 25 °C, activity of reactive species of 1 or ideal solution of 1.0 mol L-1, and equilibrium potential of any other state. 

As, Sn, Bi, and Sb dissolve anodically but will precipitate in the electrolyte as oxide or hydroxide compounds and form part of the anode slime. Because the standard electrode potentials of Bi, Sb, and As are very close to that of copper, they may deposit on the Cu cathode and affect cathode quality. 

The deposition of copper necessarily occurs at the cathode. Since there is no more easily oxidizable species than water in the system, O will evolve at the anode. The two half-reactions and their corresponding standard electrode potentials are (see Table 18-1)... 

The SHE functions as the anode in this cell, and Cu ions oxidize H2 to H+ ions. The standard electrode potential of the copper half-cell is 0.337 volt as a cathode in the Cu-SHE cell. 

Kilmartin and Wright [97K1L/WRI] recently studied the development of thin CuSeCN(s) layers on metallic copper in 0.1 M SeCN solutions by cyclic voltammetry. The peaks observed were assumed to relate to the formation and removal of CuSeCN(s) according to the reaction Cu(cr) + SeCN CuSeCN(s) + e . The shapes of the volt-ammograms do, however, indicate that the electrode reaction exhibits non-Nemstian behaviour. The authors also noted that during their experiments, a possible formation of elemental selenium occurred on the electrode surface. Therefore, the recorded electrode potential characteristics cannot be regarded as well established and these data cannot be used for calculating the standard electrode potential of the above redox couple and the solubility product of CuSeCN(cr). 

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