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Document Type

Original Article

Subject Areas



Potentiometric; platinum; silver; tantalum; Passive films; Indicator; Titration


Tantalum metalwas found to serve as an excellent indicator for potentiometric precipitation titrations. The experimental results were discussed in terms of the potential arrests and potential shifts upon addition of the titrant. The obtained results for 0.05M halogen solutions revealed that when tantalum electrode is coupled with SCE or Pt electrodes, sharp potential jumps and distinct end points were obtained in the titration of Clֿ, Brֿ and Iֿ solutions against 0.057M AgNO3 solution in both forward and backward titration techniques. On the other hand, Ta/Ag systems in forward titrations of Brֿ and Clֿ solutions behave similarly. While in backward titration, the end point is determined by presence of a sharp potential peak in the positive direction. In Iֿ solutions, Ta/Ag system illustrates a sharp potential peak in both forward and backward titration curves. Results for 0.1M halogen solutions revealed that the equivalence volumes in forward titrations for Brֿ and Iֿ solutions in the four systems are very near to the calculated ones. Concerning Clֿ solutions, the volume magnitudes corresponding to the potential jumps are so far from calculated values in all systems used. For Iֿ solution, in backward titration, the order of increasing potential jumps of tantalum systems was as follows: Ta/ Pt < Ta/ Ag < Ta/SCE system. The shape of the titration curves depends upon the kind of halogen and its concentration as well as on the type of system used and type of titration when the experiment is carried out.

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