Introduction Det 3

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c20j potentiometric lab

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Introduction Det 3

  1. 1. Introduction This experiment was done to introduce young analysts to the use of electrochemical instrumentation in analytical chemistry, specifically, potentiometric end-point detection. The objective of the experiment is to analyse a mixed acid solution containing a strong acid HCl and a weak acid CH3COOH. In the analysis of the solution by potentiometric titration, it is possible to assess the appropriateness of the various end point detection techniques – the Gran plot, the first derivative (δpH/δV) and the second derivative plot (δ2pH/δV2). Potentiometric titration involves the measurement of the potential of a suitable indicator electrode as a function of titrant volume. The data provided by potentiometric titrations are particularly more reliable than the data from titrations that use chemical indicators. This is due to the fact that the procedure involves measuring and recording cell potential (in pH) after each addition of reagent and the increments of addition shifting from large to small as the end point is approached. The accuracy with which the end point can be found by potentiometric titration depends upon the magnitude of the change in the electromotive force (emf) in the region of the equivalence point. This depends upon the concentration and strength of the reagents involved – acids and alkali in this case. 2

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