Introduction
Using a suitable electrode that reacts to the concentration change during the titration, one can quantify the
change in potential in a potentiometric titration. An indicator electrode is an electrode that reacts to a
change in the amount of ions present in the solution. The reference electrode, whose potential remains
constant during the titration, is paired with the indicator electrode to create a cell. The cell's e.m.f.
varies gradually up until the end point, then quickly right before it and again gradually after. The first
derivative curve is plotted against V, the peak of which is (∆E/∆V).
The titration's end point is indicated by the curve.
Cr6+ + 3Fe2+
→ 3Fe3+ + Cr3+ [Acidic Medium]
The potentiometric titration of FAS (Mohr’s salt) solution with K2Cr2O7 in the presence of H2SO4 is a redox
titration. An oxidation-reduction electrode forms when the same material is present in both its reduced and
oxidized forms in a solution. This electrode potential can be detected by dipping a platinum wire into the
solution. Because of this, the solution contains both Fe2+ and Fe2+ ions when the titration is started,
creating an electrode potential that a Pt wire detects. The indicator electrode, then, is (Pt/Fe3+, Fe2+),
and its electrode potential is provided by,
E=E0 + 2.303 RT log (Fe3+)/ nF (Fe2+)