Redox Titrations Tutorial
- A redox titration is a volumetric method that relies on the oxidation of the analyte (substance to be analysed).
- The titrant (solution of known concentration) is often an oxidising agent.
Common oxidising agents are:
(i) permanganate ion (MnO4-)
MnO4-(aq) + 8H+ + 5e- → Mn2+(aq) + 4H2O Eo = +1.51 V
purple permanganate ion (MnO4-) is reduced to colourless manganese(II) ion (Mn2+)
(ii) dichromate ion (Cr2O72-)
Cr2O72-(aq) + 14H+ + 6e- → 2Cr3+(aq) + 7H2O Eo = +1.23 V
orange dichromate ion (Cr2O72-) is reduced to green chromium(III) ions (Cr3+)
- At the equivalence point E(forward) = E(reverse), or, ΔE(cell) = 0
- If the redox reaction does not produce a well-defined colour change at the equivalence point, an indicator should be used in the titration.
Starch can be used as an indicator for redox titrations using iodine as the titrant (iodine is a weak oxidising agent) because starch forms a blue complex with iodine.
- The redox titration curve is a plot of Electrode Potential (volts) vs volume of titrant or analyte.
- Redox titrations can be used to determine the concentration of: