Simple Oxidation-Reduction Titrations

We can obtain the number of moles of Ce4+ ions from the volume and molarity of the Ce4+ solution used as the titrant  

The number of moles of Sn2+ ions can be obtained by applying the appropriate mole ratio from the balanced equation  

This value represents the quantity of Sn2+ ions in 1.00 L of solution. Thus the concentration of Sn2+ in the unknown solution is 

Permanganate being introduced into a flask of reducing agent. 

The strong oxidizing agent, the permanganate ion (Mn04 ), can undergo several different reactions. The reaction that occurs in acidic solution is the one most commonly used  

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Simple Oxidation-Reduction Titrations 130 Discussion Questions and Exercises 131... 

In Sections 10.11-10.16 it is shown how the change in pH during acid-base titrations may be calculated, and how the titration curves thus obtained can be used (a) to ascertain the most suitable indicator to be used in a given titration, and (b) to determine the titration error. Similar procedures may be carried out for oxidation-reduction titrations. Consider first a simple case which involves only change in ionic charge, and is theoretically independent of the hydrogen-ion concentration. A suitable example, for purposes of illustration, is the titration of 100 mL of 0.1M iron(II) with 0.1M cerium(IV) in the presence of dilute sulphuric acid ... 

In addition, potentiometric titration methods exist in which an electrode other than an ion-selective electrode is used. A simple platinum wire surface can be used as the indicator electrode when an oxidation-reduction reaction occurs in the titration vessel. An example is the reaction of Ce(IV) with Fe(II) ... 

The standard potential of the indicator system is not known exactly, but experiments have shown that in not too strongly acid solutions the sharp color change from colorless to violet, with green as a possible intermediate, occurs at a potential of about — 0.75 volt. The standard potential of the ferrous-ferric system is 0.78 whereas that of the di-chromate-chromic ion system in an acid medium is approximately — 1.2 volt hence a suitable oxidation-reduction indicator might be expected to have a standard potential of about — 0.95 volt. It would thus appear that diphenylamine would not be satisfactory for the titration of ferrous ions by acid dichromate, and this is actually true if a simple ferrous salt is employed. In actual practice, for titration purposes, phosphoric acid or a fluoride is added to the solution these substances form complex ions with the ferric ions with the result that the effective standard potential of the ferrous-ferric system is lowered (numerically) to about — 0.5 volt. The change of potential at the end-point of the titration is thus from about — 0.6 to — 1.1 volt, and hence diphenylamine, changing color in the vicinity of — 0.75 volt, is a satisfactory indicator. 

REDOX titrations are titrations that involve the processes of oxidation and reduction. These two processes always occur together and are of huge importance in chemistry. Everything from simple ionic reactions to the generation of energy within human mitochondria depends on these two processes. 

The change in oxidation potential during the titration of a reductant (iron(II)) by an oxidant (ceri-um(IV)) is shown in Figure 5. The final oxidation potential increases with the strength of the oxidant used. Sometimes, it is possible to make a simple calculation of the equivalence potential (Epp) as follows. For the reaction that can be written as in [XVII] ... 

C60 with strong acids, a C q solution was generated by controlled potential electrolysis and titrated with concentrated triflic acid. UV/visible-near IR spectra as well as steady state voltammetry with ultramicroelectrodes were used to monitor 50 and C60H. Addition of the triflic acid led to a decrease of absorbance and steady state oxidation current of Cgo". At the same time, a reduction current appeared at potentials more negative than the half wave potential of Cgg oxidation. This current was attributed to CeoH reduction. With some simple assumptions, the current changes were used to calculate the equilibrium constant of the reaction ... 

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