Potentiometric Titrations Indirect Potentiometry

One of the most fruitful uses of potentiometry in analytical chemistry is its apphcation to titrimetry. Prior to this apphcation, most titrations were carried 

Some text in this section is taken from Analjdical Chemistry , James G. Dick, McGraw-HiU, Inc., (1973), Chapter 12 (with permission). 

The indicator endpoint may or may not represent the equivalence point of the titration. Where it does not, indicator blanks are usually required. Depending on the nature of the indicator and the conditions of the titration reaction, these blanks can be quite substantial. 

Titrations requiring the use of colour-change indicators often suffer from the lack of an indicator reacting in the equivalence point zone required. There is no lack of indicators to chose from for neutralisation titrations there is often, however, a lack of indicator choices to meet the requirements of precipitation, complexation and oxidation-reduction titrations. 

The indicator colour change may be easily obscured where coloured solutions must be titrated, where the solution is turbid or where a coloured precipitate is the product of the titration reaction. 

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The measurement of pK for bases as weak as thiazoles can be undertaken in two ways by potentiometric titration and by absorption spectrophotometry. In the cases of thiazoles, the second method has been used (140, 148-150). A certain number of anomalies in the results obtained by potentiometry in aqueous medium using Henderson s classical equation directly have led to the development of an indirect method of treatment of the experimental results, while keeping the Henderson equation (144). 

One of the most fruitful uses of potentiometry in analytical chemistry is its application to titrimetry. Prior to this application, most titrations were carried out using colour-change indicators to signal the titration endpoint. A potentiometric titration (or indirect potentiometry) involves measurement of the potential of a suitable indicator electrode as a function of titrant volume. The information provided by a potentiometric titration is not the same as that obtained from a direct potentiometric measurement. As pointed out by Dick [473], there are advantages to potentiometric titration over direct potentiometry, despite the fact that the two techniques very often use the same type of electrodes. Potentiometric titrations provide data that are more reliable than data from titrations that use chemical indicators, but potentiometric titrations are more time-consuming. 

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