Redox potential worked example

Worked Example 7.9 Consider the electrode potentials for metallic lead within a lead-acid battery. The lead has three common redox states, Pb4+, Pb2+ and Pb°, so there are three possible equilibria to consider ... 

A final example of the use of dithiolenes comes from the work of Grimaldi and Lehn,222 and Ohki, Tagaki and Ueno.223 These groups used tetraphenylnickeldithiolene as a redox potential driven electron carrier and cation carrier through artificial membranes. Lipophilic cocarriers were employed to generate a multicomponent carrier system, in which charge equalization occurs. Applications to biomembranes, ion separation and related processes were suggested. 

Because the potential of an electrochemical cell depends on the concentrations of the participating ions, the observed potential can be used as a sensitive method for measuring ion concentrations in solution. We have already mentioned the ion-selective electrodes that work by this principle. Another application of the relationship between cell potential and concentration is the determination of equilibrium constants for reactions that are not redox reactions. For example, consider a modified version of the silver concentration cell shown in Fig. 11.11. If the 0.10 M AgN03 solution in the left-hand compartment is replaced by 1.0 M NaCl and an excess of solid AgCl is added to the cell, the observed cell potential can be used to determine the concentration of Ag+ in equilibrium with the AgCl(s). In other words, at 25°C we can write the Nernst equation as... 

For the Cr /Cr couple, Ff = —0.41 V, and Cr(II) compounds slowly liberate H2 from water, as well as undergo oxidation by O2 (see worked example 7.4). The potential diagram in Figure 21.9 shows that Cr(II) compounds are just stable with respect to disproportionation. The study of the oxidation of Cr + species has played an important role in establishing the mechanisms of redox reactions (see Chapter 25). 

Liquid interfaces can work not only as catalysts or inhibitors of redox reactions, but they can also shift the Gibbs free energy or redox potentials from the values found in a homogeneous medium. For example, at the oil/water interface the following redox reaction can occur ... 

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