Redox Titrations Overview

Lecture Title: Applications of Redox Titrations

• Lecture Aim:
  • Explain oxidation-reduction (redox) reactions, including oxidation states and electron transfer concepts.
  • Introduce different types of redox titrations and discuss their performance.
  • Demonstrate how redox titrations are used for quantitative analysis to determine the concentration of oxidizing or reducing agents in a solution.

Lecture Competencies

• Knowledge of Redox Principles: Understand the concepts of oxidation and reduction, and identify oxidizing and reducing agents.
• Data Analysis and Interpretation: Analyze titration data, including construction and interpretation of titration curves, and calculate concentrations and equivalents from titration results.
• Application of Theoretical Concepts: Apply stoichiometric principles to solve redox reaction problems and relate results to real-world scenarios, such as chemistry, environmental science, and medicine.
• Critical Thinking and Problem Solving: Evaluate experimental designs and troubleshoot issues during titrations, and assess the reliability and limitations of redox titration methods.

Lecture Contents: Free Elements

• Metallic Iron (Fe): Determined by dissolving in ferric chloride solution. The resulting ferrous chloride is titrated with standard permanganate in the presence of Zimmermann reagent. Iron oxides do not interfere.
• Free Halogens (Oxidizing): Iodine determination by direct titration with sodium thiosulfate solution. Bromine or chlorine displaces iodine from potassium iodide.

Lecture Contents: Determination of Peroxides

• Hydrogen Peroxide (H₂O₂):
  • Reducing agent: Determined by direct titration using cerium(IV) ion (Ce⁴⁺) with ferroin indicator.
  • Oxidizing agent: Determined by direct titration with potassium permanganate (KMnO₄) (iodometrically).
• Zinc peroxide (ZnO₂): Determined using starch as indicator.

Lecture Contents: Determination of Organic Peroxides

• Carbamide peroxide: Topical antiseptic solution, assayed for H₂O₂ content iodometrically.
• Hydrous benzoyl peroxide: Keratolytic and keratogenic agents, determined iodometrically.

Lecture Contents: Determination of Oxides

• Higher Oxides (MnO₂, PbO₂, Pb₃O₄):
  • lodometrically: Use of acid (HCl) to determine MnO₂.
  • Indirect titration with reducing agents. Oxalic acid (C₂O₄²⁻) used with a reducing agent, like ferrous ion.
• Lead Oxide (PbO): Dissolved in glacial acetic acid, precipitating as lead oxalate; determined using KMnO₄.

Lecture Contents: Determination of Cations (Iron)

• Ferrous Salts: Determined by adding KMnO₄ after Zimmermann reagent and self indicator.
• Ferric Salts: By reduction to Fe²⁺ using pre-reductants (e.g., SnCl₂, Zn and H₂SO₄). Amalgamated zinc (ZnHg) and Jones reductor are also used.
• Direct Titration with Titanous Chloride for Fe³⁺, using methylene blue or thiocyanate as indicators.
• lodometrically: Fe³⁺/Fe²⁺ and I₂/I⁻ systems are used for determination.

Lecture Contents: Determination of Cations (Hg²⁺)

• HgCl₂: Reduced initially to Hg° by using formaldehyde (HCHO) in a Ca(OH)₂ medium. Excess standard reagent(e.g.,Na₂S₂O₃) used to indicate end point.

Lecture Contents: Determination of Insoluble Oxalates

• Cations (Ca²⁺, Ba²⁺, and others) form insoluble oxalates which are then dissolved in dilute sulfuric acid and titrated with standard KMnO₄.

Lecture Contents: Determination of Anions (Soluble Oxalates)

• Soluble oxalates are determined by using KMnO₄ or Ce⁴⁺ in the presence of sulfuric acid and heating. The slow reaction initially becomes faster after the reduction product is formed (Mn²⁺ or Ce³⁺).

Lecture Contents: Determination of Anions (Sulphides, Thiosulphates, Sulphates and others)

• Sulphide: Direct titration with I₂.
• Thiosulphate: Back titration using a known excess of I₂.
• Sulphite: Titration with I₂ and water.
• Sulphate: Treated with barium chromate (BaCrO₄), then iodometrically analyzed.

Lecture Contents: Determination of Anions (Chlorates, Hypochlorites, and others)

• Chlorates (ClO₃⁻) and Hypochlorites (ClO⁻): Iodometrically analyzed.

Lecture Contents: Determination of Organic Compounds (Vitamin C, Glycerol, Thiols etc.)

• Vitamin C (Ascorbic acid): Determined iodometrically.
• Glycerol: Determined iodometrically .
• Mercaptans (thiols): Determined iodometrically.

Lecture Contents: Determination of Moisture Content

• Karl-Fischer Reagent: Used to determine moisture content. Iodine (I₂) and sulfur dioxide (SO₂) in an anhydrous medium containing pyridine are used to determine water.

Lecture Contents: Analysis of Mixtures (Acetic, Formic, Oxalic, Phenol, and Ferrous Oxalate and others)

• Acetic and formic acids: Analysis involving hydroxide (OH⁻) and permanganate (MnO₄⁻).
• Oxalic and sulphuric acids: Analysis involving hydroxide (OH⁻) and permanganate (MnO₄⁻).
• Phenol and salicylic acids: Analysis involving bromometric or hydroxide approaches.
• Iodine (I₂) and potassium iodide (KI): Used for analyses.
• Ferrous oxalate and oxalic acid (protoxalate): Analysis using permanganate (MnO₄⁻) or iodometrically.

Lecture References

• "Analytical Chemistry" by Gary D. Christian
• "Quantitative Chemical Analysis" by Daniel C. Harris
• "Chemistry: A Molecular Approach" by Nivaldo J. Tro
• "Principles of Instrumental Analysis" by Douglas A. Skoog, F. James Holler, and Timothy A. Nieman
• "Analytical Chemistry: A Modern Approach to Analytical Science" by David Harvey