Types of redox titrations

Redox titrations are of various types, including permanganate, dichromate, iodometric, and iodimetric titrations.

1. Cerimetry:

Principle:
- Cerimetry involves the use of cerium(IV) salts, such as cerium(IV) sulfate, as the oxidizing titrant.
- In this process, cerium(IV) ions are reduced to cerium(III) ions when they react with reducing agents in the analyte.
Applications:
- Cerimetry is used to determine reducing sugars, phenols, and various organic and inorganic substances.
Example Chemical Reaction:
- The oxidation of oxalic acid by cerium(IV) sulfate:
2{Ce(SO4)2} + {C2H2O4} -> 2{Ce(SO4)2} + 2{H2SO4} + 2{CO2}

Principle:
- Iodimetry involves the direct titration of a reducing agent with iodine (I₂) as the oxidizing titrant. Iodine is reduced to iodide (I⁻), while the reducing agent is oxidized.
Applications:
- Iodimetry is used to quantify reducing agents like sulfites, thiosulfates, arsenites, and organic compounds such as vitamin C.
Example Chemical Reaction:
- In the iodimetric titration of sodium thiosulfate (Na₂S₂O₃), iodine reacts with thiosulfate ions to produce tetrathionate and iodide:
- $2{S2O3^{2-}} +{I2} ->{S4O6^{2-}} + 2{I^-}$
Principle:
- Iodimetry involves the direct titration of a reducing agent with iodine (I2) as the oxidizing titrant.
- In this process, iodine is reduced to iodide (I-) ions, while the reducing agent is oxidized.
Applications:
- Iodimetry is used to determine the concentration of reducing agents such as sulphites, thiosulfates, arsenites, and some organic compounds like vitamin C.
Example chemical reaction:
- In the iodimetric titration of sodium thiosulfate (Na2S2O3), iodine reacts with the thiosulfate ions (S2O3^2-) to produce tetrathionate ions (S4O6^2-) and iodide ions (I-):
  - 2 S2O3^2- + I2 → S4O6^2- + 2 I-

Principle:
- Iodometry is an indirect redox titration where the reducing agent reacts with excess iodine, producing iodide ions.
- The unreacted iodine is then titrated with sodium thiosulfate.
Applications:
- Iodometry is used for the determination of metal ions like copper and antimony, as well as various organic and pharmaceutical substances.
Example Chemical Reaction:
- In the iodometric determination of copper(II) ions, copper(II) sulfate reacts with potassium iodide to produce copper(I) iodide and iodine.
- The liberated iodine is titrated with sodium thiosulfate:
- ${Cu}^{2+} + 2{I}^-+{I}_2$
- $2{S}_{2}{O}_{3}^{2-} +{I}_2 {S}_{4}\mathrm{O}_{6}^{2-} + 2{I}^-$
- The overall reaction:
- ${Cu}^{2+} + 2{S}_{2}\mathrm{O}_{3}^{2-}{Cu}^+\{S}_{4}\mathrm{O}_{6}^{2-}$

Principle:
- Bromatometry is similar to iodimetry but uses bromine (Br₂) as the oxidizing titrant.
- Bromine reacts with reducing agents to form bromide (Br⁻) ions.
Applications:
- Bromatometry is employed to determine reducing agents like ascorbic acid, hydroquinone, phenols, and for the analysis of pharmaceuticals, food products, and environmental samples.
Example Chemical Reaction:
- In the bromatometric titration of ascorbic acid (vitamin C, C₆H₈O₆), bromine reacts with ascorbic acid to form dehydroascorbic acid and bromide:
- $\mathrm{C}_6\mathrm{H}_8\mathrm{O}_6 + \mathrm{Br}_2 \rightarrow \mathrm{C}_6\mathrm{H}_6\mathrm{O}_6 + 2\mathrm{HBr}$

Principle:
- Dichrometry uses potassium dichromate (K₂Cr₂O₇) or sodium dichromate (Na₂Cr₂O₇) as the oxidizing titrant. Dichromate ions (Cr₂O₇²⁻) are reduced to chromium (III) ions (Cr³⁺) when they react with reducing agents.
Applications:
- Dichrometry is used to determine ferrous ions (Fe²⁺), oxalic acid, and other reducing agents.
- It is also applied in environmental sample analysis (e.g., wastewater) and industrial quality control.
Example Chemical Reaction:
- In the dichrometric titration of ferrous ammonium sulfate, potassium dichromate reacts with ferrous ions to produce ferric ions and chromium (III) ions in an acidic medium:
- $\mathrm{Cr}_2\mathrm{O}_7^{2-} + 6\mathrm{Fe}^{2+} + 14\mathrm{H}^+ \rightarrow 2\mathrm{Cr}^{3+} + 6\mathrm{Fe}^{3+} + 7\mathrm{H}_2\mathrm{O}$
- $\mathrm{Cr}_2\mathrm{O}_7^{2-} + 6\mathrm{Fe}^{2+} + 14\mathrm{H}^+ \rightarrow 2\mathrm{Cr}^{3+} + 6\mathrm{Fe}^{3+} + 7\mathrm{H}_2\mathrm{O}$

Principle:
- In potassium iodate titrations, iodate ions (IO₃⁻) are reduced to iodide ions (I⁻), while the analyte is oxidized. Alternatively, iodate reacts with iodide to produce iodine, which then reacts with the analyte.
Applications:
- Potassium iodate titrations are used for the determination of reducing substances like arsenic (III), sulfur dioxide, sulfite ions, and antioxidants in food and pharmaceuticals.
Example Chemical Reaction:
- In the titration of sulfite ions (SO₃²⁻) with potassium iodate, iodate ions first react with iodide ions to produce iodine, which then reacts with the sulfite ions to form sulfate and iodide:
- $\mathrm{IO}_3^- + 5\mathrm{I}^- + 6\mathrm{H}^+ \rightarrow 3\mathrm{I}_2 + 3\mathrm{H}_2\mathrm{O}$
- $\mathrm{I}_2 + \mathrm{SO}_3^{2-} + 2\mathrm{H}_2\mathrm{O} \rightarrow 2\mathrm{I}^- + \mathrm{SO}_4^{2-} + 4\mathrm{H}^+$
- The overall reaction:
- $\mathrm{IO}_3^- + 3\mathrm{SO}_3^{2-} + 2\mathrm{H}^+ \rightarrow 3\mathrm{SO}_4^{2-} + 2\mathrm{I}^- + \mathrm{H}_2\mathrm{O}$