TANTALUM AS AN INDICATOR ELECTRODE IN DIFFERENT POTENTIOMETRIC TITRATIONS

Tantalum metal was employed as an indicator electrode in different potentiometric titrations. Silver, platinum and SCE were successfully applied as reference electrodes. A number of classical acid/base reactions were chosen. This involve titration of strong and weak mono- and poly basic acids; HCl, H2SO4, H3PO4, HCOOH and H2C2O4 with NaOH and NH4OH. Both forward and backward titrations were carried out. The titration performed until the greatest jump of potential appeared by adding one drop of titrant. Both forward and backward titration curves showed marked potential inflexions which recorded at the theoretically calculated equivalence points. Bimetallic combinations were equally suitable for the determination of equivalence points of acids neutralizing in more than one step, e.g., H3PO4 but not with oxalic acid.
The titrations of S2O3ֿֿwith I2 solutionusing the different tantalum systems were equally successful; sharp potential jumps and distinct end points were obtained. Moreover the potential changes at the same direction as that of Pt/SCE system. On the other hand, when ferrous iron reacted with permanganate, a Ta/Pt system gave a potential responsive to Fe+2 concentrations. The titration curves obtained exhibited regular defined and sharp inflexion points with high potential drop at the equivalence point. This potential drop had a reverse direction compared with that of Pt/SCE system. While on titrating Fe++ ions with dichromate solution, the curves had no distinct end points at any of the examined systems. These systems successes also to define the end point in the titration of FeCl3 against NaOH solution.