A convenient and useful method of determining the equivalence point of a titration, i.e the point at which the stoichiometric analytical reaction is complete, results from the use of electrochemical measurements. If an indicator electrode, sensitive to the concentration of the chemical undergoing titrimetric reaction, and a reference electrode, whose potential is not sensitive to any dissolved chemical in solution, are immersed in the solution under examination to form a galvanic cell, the potential difference between the electrodes may be sensed by a simple potentiometer or electronic device and used to follow the course of the reaction. If a graph of the variation of potential difference is plotted as a function of the quantity of the titrant added, a sigmoid curve results with a rapidly changing portion in the vicinity of the equivalence point. The midpoint of this linear vertical portion or the inflection point may be taken as the endpoint of the titration.
Related: Calibration of Automatic Potentiometric Titrator
The apparatus used comprises a voltmeter allowing readings to the nearest millivolt. The choice of the electrode system is governed by the nature of the titration. Table 1 summaries several acceptable electrode systems. Automatic titrators are commonly employed these days. Two types of instruments are available. In the first one addition of titrant is carried out automatically and the electrode potential differences during the course of titration are recorded as the expected sigmoid curve. In the second type, titrant addition is performed automatically until or preset potential or pH, representing the end - point, is reached when the addition of the titrant ceases.
Related: Calibration of Automatic Potentiometric Titrator
Apparatus
The apparatus used comprises a voltmeter allowing readings to the nearest millivolt. The choice of the electrode system is governed by the nature of the titration. Table 1 summaries several acceptable electrode systems. Automatic titrators are commonly employed these days. Two types of instruments are available. In the first one addition of titrant is carried out automatically and the electrode potential differences during the course of titration are recorded as the expected sigmoid curve. In the second type, titrant addition is performed automatically until or preset potential or pH, representing the end - point, is reached when the addition of the titrant ceases.
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ReplyDeleteplease provide the electrode maintainance of all the potentiometric titrations