Titration precipitation titrations

The study of nonaqueous titrations covers a very broad field. It can include acid-base titrations, oxidation-reduction titrations, precipitation-titrations, and titrations involving complex formation. In order to limit things somewhat, I would like to discuss only nonaqueous acid-base titrations. However, I do not mean to imply that other types of titrations carried out in nonaqueous media are of lesser importance. For example, some excellent oxidation-reduction titrations have been carried out by Dr. Stone of Michigan State and as an example of a precipitation titration, we developed a method several years ago for titrating sulfate with barium that is carried out at least partly in nonaqueous solution. Other examples could be given but to mention all of them would lead to an excessively prolonged discussion. 

Table 11.30 lists standard solutions for precipitation titrations and Table 11.31 lists specific reagents as indicators, adsorption indicators, and protective colloids for precipitation titrations. 

The list given below includes the substances that are most used and most useful for the standardization of solutions for precipitation titrations. Primary standard solutions are denoted by the letter (P) in Column 1. 

Examples of titration curves for (a) a complexation titration, (b) a redox titration, and (c) a precipitation titration. 

Thus far we have examined titrimetric methods based on acid-base, complexation, and redox reactions. A reaction in which the analyte and titrant form an insoluble precipitate also can form the basis for a titration. We call this type of titration a precipitation titration. 

The titration curve for a precipitation titration follows the change in either the analyte s or titrant s concentration as a function of the volume of titrant. For example, in an analysis for V using Ag+ as a titrant... 

Sketching the Titration Curve As we have done for acid-base, complexometric titrations, and redox titrations, we now show how to quickly sketch a precipitation titration curve using a minimum number of calculations. 

How to sketch a precipitation titration curve see text for explanation. 

Initial attempts at developing precipitation titration methods were limited by a poor end point signal. Finding the end point by looking for the first addition of titrant that does not yield additional precipitate is cumbersome at best. The feasibility of precipitation titrimetry improved with the development of visual indicators and potentiometric ion-selective electrodes. 

Finding the End Point Potcntiomctrically Another method for locating the end point of a precipitation titration is to monitor the change in concentration for the analyte or titrant using an ion-selective electrode. The end point can then be found from a visual inspection of the titration curve. A further discussion of potentiome-try is found in Chapter 11. 

Precipitation titrimetry is rarely listed as a standard method of analysis, but may still be useful as a secondary analytical method for verifying results obtained by other methods. Most precipitation titrations involve Ag+ as either an analyte or... 

The scale of operations, accuracy, precision, sensitivity, time, and cost of methods involving precipitation titrations are similar to those described earlier in the chapter for other titrimetric methods. Precipitation titrations also can be extended to the analysis of mixtures, provided that there is a significant difference in the solubilities of the precipitates. Figure 9.43 shows an example of the titration curve for a mixture of % and Ch using Ag+ as a titrant. 

Einally, the last experiment describes an unustml precipitation titration. 

The reaction of a positively charged polyelectrolyte with a negatively charged polyelectrolyte produces a precipitate, forming the basis for a precipitation titration. This paper provides an overview of colloid titrations, discussing... 

Potcntiomctric Titrations In Chapter 9 we noted that one method for determining the equivalence point of an acid-base titration is to follow the change in pH with a pH electrode. The potentiometric determination of equivalence points is feasible for acid-base, complexation, redox, and precipitation titrations, as well as for titrations in aqueous and nonaqueous solvents. Acid-base, complexation, and precipitation potentiometric titrations are usually monitored with an ion-selective electrode that is selective for the analyte, although an electrode that is selective for the titrant or a reaction product also can be used. A redox electrode, such as a Pt wire, and a reference electrode are used for potentiometric redox titrations. More details about potentiometric titrations are found in Chapter 9. 

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