Total systematic error in redox titrations with visual indicators--I: basic principles.
The following factors contribute to the total error in redox titrations with visual indicators: the end-point error (DeltaV(T)), which arises from the difference between the potential of the equivalence point and that of the actual end-point determined by a given indicator ; the indicator consumption error (DeltaV(T)), which arises from the amount of indicator oxidized (or reduced) by the titrant; the irreversibility error, which is in fact a part of the indicator consumption error, arising from the generally uncontrolled processes connected with the irreversibility of the redox processes, decomposition of the reaction products, etc. The first two factors can be evaluated on the basis of the physicochemical characteristics of all the systems involved. They contribute to the total systematic error. The third, being not strictly controlled, in general increases the positive indicator consumption error, depending on such parameters as rate of titrant addition, stirring, effect of decomposition products on the potential, etc.
Hulanicki
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Institute of Fundamental Problems in Chemistry, University, Warsaw, Poland.
Głab
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