Vanadium is an environmental pollutant originating from some types of steel, but
also from the combustion of fossil fuels. The amount of V2+ in an unknown sample is
determined by potentiometric titration by 7.62 mM permanganate ion, MnO4
-
. 25.00 mL of
unknown was titrated with 12.38 mL of 7.62 mM MnO4
- using a SCE reference electrode (Eref =
0.241 V). pH of the solution was maintained at pH = 4.00. Determine the potential at the
equivalence point and the concentration of vanadium in the unknown sample.
V3+ + e- → V2+ Eo = -0.255 V
MnO4
- + 8H+ + 5e- → Mn2+ + 4 H2O Eo = +1.507 V