Chlorine standard electrode potential

Table 3.3 Standard electrode potentials in eutectic melts referred to a chlorine reference electrode. (According to R. W. Laity)... 

Chlorine reactions may be classified broadly under two types (i) oxidation-reduction and (ii) substitution reactions. The standard electrode potential for Cr — V2CI2 + e in aqueous solution is -1.36 V. Some examples of both types are highlighted briefly below ... 

Passage of 1.0 mol of electrons (one faraday, 96,485 A s) will produce 1.0 mol of oxidation or reduction—in this case, 1.0 mol of Cl- converted to 0.5 mol of Cl2, and 1.0 mol of water reduced to 1.0 mol of OH- plus 0.5 mol of H2. Thermodynamically, the electrical potential required to do this is given by the difference in standard electrode potentials (Chapter 15 and Appendix D) for the anode and cathode processes, but there is also an additional voltage or overpotential that originates in kinetic barriers within these multistep gas-evolving electrode processes. The overpotential can be minimized by catalyzing the electrode reactions in the case of chlorine evolution, this can be done by coating the anode with ruthenium dioxide. 

Apparent Standard Electrode Potentials with Respect to THE Chlorine Electrode in 1 1 Mole KCl NaCl< ... 

It is perhaps helpful at this stage to look at the reactions which free iron ions catalyze. This is chemistry which was originally developed by Fenton in 1894 in order to improve the oxidizing power of hydrogen peroxide by the production of hydroxyl radicals, OH , which have a standard electrode potential of 2.8 V which is more positive than those of ozone, hydrogen peroxide itself (1.8 V) potassium permanganate and chlorine and only marginally less than the standard reduc-... 

This has a standard electrode potential of+0.4 V. The difference between the potentials of Eqs (99) and (101) is the 1.23 V of Eq. (100). In a chlorine cell operating at 95% current efficiency, the difference between the two possible cathode reactions is equivalent to 980kWhrt-i CI2. 

Although Equation 9.5 has the lower equilibrium potential there is a significant oveipotential of at least 0.5 volts depending on the nature of the anode. This then favours the formation of Pb02 over oxygen. In the case of chloride the standard potential for chlorine formation is -1.36 volts with little overpotential and hence this reaction is favoured. If ferrous iron is present then oxidation at the anode in accordance with Equation 9.6 has a standard electrode potential of -0.7 volts and this reaction will predominate. 

Use electrode potentials to answer the following questions, assuming standard conditions, (a) Do you expect permanganate ion (Mn04 ) to oxidize chloride ion to chlorine gas in acidic solution (b) Will dichromate ion (Cr207 ) oxidize chloride ion to chlorine gas in acidic solution ... 

It should be remembered that the standard potential refers to the condition in which all the substances in the cell are in their standard states of unit activity. Gases such as hydrogen, oxygen and chlorine are thus at 1 atm. pressure. With bromine and iodine, however, the standard states are chosen as the pure liquid and solid, respectively the solutions are therefore saturated with these elements in the standard electrodes. For all ions the standard state of unit activity is taken as the hypothetical ideal solution of unit molality or, in other words, a solution for which the product my is unity, where m is the molality of the ion and y its activity coefficient. 

Several investigations have been made of the reduction of cobalt(II) to cobalt(O) in molten salt media. Eor a eutectic melt of LiCl-KCl at 450°C[10], a 1 1 NaCl-KCl melt at 450°C[11], and a MgCh-NaCl-KCl (50 30 20 mol%) mixture at 475 °C [12], the apparent standard potentials for the cobalt(II)-cobalt(0) couple have been deduced to be —1.207 V, — 1.277 V, and—1.046 V, respectively, each with respect to a chlorine-chloride ion reference electrode. 

These equations refer to one-electron reductions versus the standard hydrogen electrode. Substrates M with more positive reduction potentials for the couple M/ M are stronger oxidants than substrates with lower or negative E. Therefore, in this case, M is easier to reduce. Eor example, the couple Cl /Cr has a reduction potential E of 2.200 to 2.600 V, and therefore chloride ions can theoretically be oxidized in water to chlorine atoms by hydroxyl radicals with E( OH, H / H20) = 2.730 V, according to Eq. 6-3 ... 

The standard e.m.f. of this cell as given by equation (25), with the pressure in atmospheres, is the difference between the standard potentials of the ChCl atm.), Cl and the Hg, Hg2Cl2(s), Cl electrodes since the latter is known to be — 0.2680 volt at 25 , the value of the former could be obtained provided of the cell under consideration were available. This cell is, in fact, identical with the one for which measurements are given on page 222, and the results in the last column of Table XLVIII are actually the values of required by equation (25) above. It follows, therefore, taking a mean result of — 1.090 volts at 25 for that the standard potential of the chlorine electrode is — 1.090 0.2680, i.e., - 1.358 volts at 25 . 

Amalgam Cell Starting with the chlorine electrode, the reversible standard potential is +1.37 V (all potentials are given versus NHE), due to the sodium concentration of 6 mol L-1 we have to note +1.33 V. The current-overpotential curve represents an unhindered process... 

To calculate the standard potential of an anion electrode two methods have been used. The first is possible if the heat of formation from its elements of the corresponding acid in dilute aqueous solution is available. In order to illustrate the procedure the standard potential of the chlorine electrode will be calculated. For the reaction... 

Since the standard free energies of formation of the solid sodium and the chlorine gas are both zero, this result represents the sum of the free energies of formation of the sodium and chloride ions. The standard potential of sodium is 2.714 volt, and so the standard free energy of formation of the sodium ion is — 1 X 23,070 X 2.714, i.e., — 62,600 cal. The standard free energy of formation of the chloride ion is therefore, — 94,000 (— 62,600), i.e., — 31,400 cal., and the corresponding potential would be — 1.36 volts at 25 C. This method has been used for de- termining the standard potential of the Pt, Fs(f) electrode, for which direct measurements have not been made. 

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