For redox titrations

Standard substances - continued for redox titrations - continued iodine, 384 iron, 262... 

In principle, any type of titration can be carried out conductometrically provided that during the titration a substantial change in conductance takes place before and/or after the equivalence point. This condition can be easily fulfilled in acid-base, precipitation and complex-formation titrations and also the corresponding displacement titrations, e.g., a salt of a weak acid reacting with a strong acid or a metal in a fairly stable complex reacting with an anion to yield a very stable complex. However, for redox titrations such a condition is rarely met. 

In fact, any type of titration can be carried out potentiometrically provided that an indicator electrode is applied whose potential changes markedly at the equivalence point. As the potential is a selective property of both reactants (titrand and titrant), notwithstanding an appreciable influence by the titration medium [aqueous or non-aqueous, with or without an ISA (ionic strength adjuster) or pH buffer, etc.] on that property, potentiometric titration is far more important than conductometric titration. Moreover, the potentiometric method has greater applicability because it is used not only for acid-base, precipitation, complex-formation and displacement titrations, but also for redox titrations. 

If a complete reaction implies a value of 10, which systems are suitable for redox titrations of this type, i.e. what is the relationship between o,r of the two half cells and K ... 

Acid-base, redox, precipitation and chelometric titrations are usually dealt with in textbooks on analytical chemistry. The titration curves in these titrations can be obtained potentiometrically by use of appropriate indicator electrodes, i.e. a pH-glass electrode or pH-ISFET for acid-base titrations, a platinum electrode for redox titrations, a silver electrode or ISEs for precipitation titrations, and ISEs for... 

The Student Web Site, www.whfreeman.com/cica7e, has directions for experiments that may be reproduced for your use. At this Web site, you will also find lists of experiments from the Journal of Chemical Education, a few downloadable Excel spreadsheets, and a few Living Graph Java applets that allow students to manipulate graphs by altering data points and variables. Supplementary topics at the Web site include spreadsheets for precipitation titrations, microequilibrium constants, spreadsheets for redox titration curves, and analysis of variance. 

Common Oxidizing Agents for Redox Titrations Table 1.6.4... 

An important question is whether we can use any indicator electrode. A redox electrode, i.e. inert in the range of potential where measurements are being done, is a possibility, especially for redox titrations. In other cases, the use of electrodes selective to the ion being titrated is better, such as pH electrodes in acid-base titrations. The method of analysis of the data obtained is, naturally, the same in all cases and independent of electrode material. 

We will use standard electrode potentials throughout the rest of this text to calculate cell potentials and equilibrium constants for redox reactions as well as to calculate data for redox titration curves. You should be aware that such calculations sometimes lead to results that are significantly different from those you would obtain in the laboratory. There are two main sources of these differences (1) the necessity of using concentrations in place of activities in the Nernst equation and (2) failure to take into account other equilibria such as dissociation, association, complex formation, and solvolysis. Measurement of electrode potentials can allow us to investigate these equilibria and determine their equilibrium constants, however. 

The Inverse Master Equation Approach for Redox Titration Curves... 

Fig. 4. (A) EPR spectra at 13 K of TSF-I subchloroplast particles at different stages of a reductive titration (B) Plot of EPR-signal amplitudes of four prominent lines for redox titrations at pHs 10 and 9. Open circles in the right panel represent the total signal amplitude generated by a combination of chemical reduction at room temperature and subsequent illumination at 77 K. Figure source Ke, Hansen and Beinert (1973) Oxidation-reduction potentiais of bound iron-suifur proteins of photosystem t. Proc Nat Acad Sci, USA 70 2042, 2043.

We can use our understanding of redox equihbria to describe titration curves for redox titrations. The shape of a titration curve can be predicted from the E° values of the analyte half-reaction and the titrant half-reaction. Roughly, the potential change in going from one side of the equivalence point to the other will be equal to the difference in the two values the potential will be near E° for the analyte half-reaction before the equivalence point and near that of the titrant half-reaction beyond the equivalence point. 

Spectrophotometric titrations have been used for redox titrations, acid-base titrations, and complexation titrations. The spectrophotometer can be used in a light scattering mode to measure the endpoint for a precipitation titration by turbidimetry. Spectrophotometric titrations can be easily automated. 

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