Reduction potentials chlorines

Bromine occurs ia the form of bromide ia seawater and ia natural brine deposits (see Chemicals frombrine). Chloride is also present. In all current methods of bromine production, chlorine, which has a higher reduction potential than bromine, is used to oxidize bromide to bromine. 

Figure 5.16. Plot of data for the external heavy-atom quenching of pyrene fluorescence in benzene at 20°C. Polaro-graphic half-wave reduction potentials Ein are used as a measure of the electron affinity of the quencher containing chlorine (O), bromine ( ), or iodine (3). From Thomaz and Stevens<148) with permission of W. A. Benjamin, New York.

By international agreement, the algebraic sign of E° for a half-cell is chosen to be the same as its electrical sign relative to the SHE. This means, in effect, that we must write the half-reactions with the electrons on the left-hand side in other words, E° values are taken to be reduction potentials. Consequently, a reagent such as chlorine that is more oxidizing than aqueous H+ (— H2) under standard conditions will have a positive E°... 

In our second example we look at the reduction of chlorinated ethenes at a nickel electrode and at the surfaces of two zero-valent metals [Fe(0), Zn(0)]. To gain insight into the rate-limiting process(es) in these cases, we consider how the relative overall reduction rates (relative to PCE) of PCE, TCE, and the three DCE isomers (see Fig. 14.15 for structures) vary as a function of two common descriptors used in QSARs, the one-electron reduction potential (EJ Fig- 14.17a) and the bond dissociation energy (DR X Fig. 14.176). In all these systems, the reduction rates were found to be significantly slower than diffusion of the compounds to the respective surfaces. Therefore, the large differences in the relative reactivities of the compounds between the systems reflect differences in the actual reaction at the metal surface. 

The electrolysis of brine is carried out on a huge scale for the industrial production of chlorine and caustic soda (sodium hydroxide). Because the reduction potential of Na+ is much higher than that of water, the latter substance undergoes decomposition at the cathode, yielding hydrogen gas and OH-. 

In all hitherto discussed instances the potentials at which the secondary process occurs, such as the liberation of hydrogen, oxygen or chlorine, were widely different from the potentials corresponding to the primary oxidation or reduction process. Sometimes this is not the case. The reduction potential of reaction SnIV -> Sn11, for example, is so close to the potential of hydrogen deposition that both processes take place even at comparatively low current densities. 

The theoretical decomposition voltage of chlorides can be calculated from the value of equilibrium oxidation potential of the chlorine electrode e t. cia1 ci-in the anolyte and the reversible reduction potential of the hydrogen electrode 7Toh- Ha. pt in alkaline catholyte. If we apply the Nemst equations for the corresponding electrochemical processes [see (XI-9) and (XI-10)] we obtain the... 

The theoretical decomposition voltage of sodium chloride may be calculated as the sum of the reversible oxidation potential of the chlorine electrode and the reversible reduction potential of the amalgam electrode. 

It was demonstrated that water electrolysis generates mixed oxidant systems. Oxidation-reduction potential (Hsu and Kao 2004) is not the best parameter for system characterisation. In general, the online analysis of generated species is an unsolved problem. Probably, not all electrolysis products are known. This can be seen in analysing the active and total chlorine concentration. The standard method uses DPD but the effect of other chemicals on the DPD method is one reason that active chlorine is sometimes incorrectly measured. Amperometric analysis and... 

The Mn(IV)(salpn)Cl2 is a good oxidant, showing a reduction potential at +890 mV versus SCE. Other highly oxidized Mn complexes that contain chlorine have been shown to chlorinate alkanes, alkenes, and... 

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 ... 

At the anode, the metal is oxidized in preference to sSf and CF anions, thereby avoiding secondary chlorination reactions (especially on aromatic rings) in an undivided cell. Normally, for the reaction to proceed, the reduction potentials of the different species present in solution must satisfy the order shown in Fig. la. 

This diminishes the HOMO-LUMO gap from the porphyrin, to the chlorin and to the bacteriochlorin, explaining the bathochromic shift of the bands. The oxidation and reduction potentials of these species follow the energy changes of the HOMO and LUMO, respectively. Thus, again within a homologous series, the reduction potentials of the porphyria, chlorin, and bacteriochlorin remain essentially the same, whereas the oxidation potentials become increasingly more facile, with... 

Electrolysis of aqueous sodium chloride (brine) is an important industrial process for the production of chlorine and sodium hydroxide. In fact, this process is second only to the production of aluminum as a consumer cf electricity in the United States. Sodium is not produced in this process under normal circumstances because H20 is more easily reduced than Na+, as the standard reduction potentials show ... 

To study the direct PET in QD-quinone heterocomposites uncapped CdSe quantum dots (dcdse =2.6 nm, without ZnS monolayers and stabilized by TOPO molecules) have been used as electron donors. Quinones with increasing electron accepting abilities 1,4-benzoquinone (1,4-BQ), tetra-chlorine-l,4-benzoquinone (tCl-l,4-BQ) and tetra-chlorine-l,2-benzoquinone (tCl-l,2-BQ) have been used as electron acceptors moieties that are characterized by low reduction potentials (Fig. 1). 

V, which is still less than 1.40 V, the reduction potential for the competing reaction involving chlorine. The cathode half-reaction now becomes... 

Chlorine residual concentrations of the water upstream and downstream of the dechloramination chemical feed points were measured using a Hach Chlorine Pocket Colorimeter. Temperature, dissolved oxygen (DO), pH, and oxidation-reduction potential (ORP) were also measured during the field study. 

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