Types of redox titrations
- S-1-PHARMACEUTICAL-ANALYSIS
- Feb 26
- 3 min read
Updated: Mar 2
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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 commonly used for the determination of reducing sugars, phenols, and a variety of 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 H2SO4 + 2 CO2
2) Iodimetry
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 the thiosulfate ions (S2O3^2-) to produce tetrathionate ions (S4O6^2-) and iodide ions (I-):
2 S2O3^2- + I2 → S4O6^2- + 2 I-
3) Iodometry
Principle
Iodometry is an indirect redox titration technique where the reducing agent reacts with excess iodine to produce iodide ions.
The unreacted iodine is then titrated with a standard thiosulfate solution.
Applications
Iodometry is used for the determination of copper, antimony, and other metal ions, as well as various organic compounds 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- → CuI + I2
2 S2O3^2- + I2 → S4O6^2- + 2 I-
The overall reaction:
Cu^2+ + 2 S2O3^2- → Cu^+ + S4O6^2-
4) Bromometry
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:
C6H8O6+Br2→C6H6O6+2HBr
Principle
Bromatometry is similar to iodimetry, but it uses bromine (Br2) as the oxidizing titrant instead of iodine.
The bromine reacts with reducing agents, forming bromide (Br-) ions in the process.
Applications
Bromatometry is employed to determine the concentration of reducing agents like ascorbic acid, hydroquinone, and phenols.
It can also be used 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 produce dehydroascorbic acid and bromide ions:
C6H8O6 + Br2 → C6H6O6 + 2 HBr
5) Dichrometry
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:
Cr2O72∓6Fe2++14H+→2Cr3++6Fe3++7H2O
6) Titration with Potassium Iodate
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:
The overall reaction:
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