redox titration B pharm 1st sem Full notes

Redox Titration

1. Redox titrations Santosh Kumar Assistant Professor Department of Pharmacy Sarala Birla University, Ranchi Email : [email protected]

2. SYLLABUS Concepts of oxidation and reduction Types of redox titrations (principles and applications) Cerimetry Iodimetry Iodometry Bromatometry Dichrometry Titration with potassium iodate

3. Definition Also known as oxidation-reduction titration. Redox titrations : These are titrations used to determine unknown reducing agents with a known amount of oxidizing agents or determine unknown oxidizing agents with a known amount of reducing agents. Oxidizing agents : Titrant in redox titrations. Redox reactions involve both reduction (RED) and oxidation (OX).

4. CONCEPTS OF OXIDATION AND REDUCTION

5. CONCEPTS OF OXIDATION AND REDUCTION When oxidation and reduction reactions occur together, they are called Redox reactions .

6. CONCEPTS OF OXIDATION AND REDUCTION Example In the reaction: Fe²⁺ → Fe³⁺ (oxidation) and Ce⁴⁺ → Ce³⁺ (reduction), Oxidation : Fe²⁺ is oxidized to Fe³⁺ Reduction : Ce⁴⁺ is reduced to Ce³⁺

7. CONCEPTS OF OXIDATION AND REDUCTION OXIDATION A reaction in which loss of electrons occurs, and the oxidation state increases . Examples Addition of Oxygen: SO₂ + O₂ → SO₃ Removal of Hydrogen: H₂S + O₂ → S + H₂O Loss of electrons (LEO): Fe²⁺ → Fe³⁺ + e⁻ REDUCTION A reaction in which gain of electrons occurs, and the oxidation state decreases . Examples Removal of Oxygen: CuO + H₂ → Cu + H₂O Addition of Hydrogen: C₂H₂ + 2H₂ → C₂H₆ Gain of electrons (GEO): Fe³⁺ + e⁻ → Fe²⁺

8. Oxidizing Agents These are substances that reduce themselves (gain electrons) and oxidize others (cause other substances to lose electrons). They are also known as oxidants . Examples Potassium dichromate ( K₂Cr₂O ₇) Potassium permanganate ( KMnO ₄) Potassium iodate (KIO₃) Hydrogen peroxide (H₂O₂)

9. Reducing Agents These substances oxidize themselves (lose electrons) and reduce others (cause other substances to gain electrons). They are also known as reductants . Examples : Ferrous thiosulphate Ferrous sulphate Oxalic acid

10. Types of Redox Indicators Internal Indicator Self Indicator External Indicator Instrumental Indicator

11. Internal Indicator These indicators are mixed directly with the solution and change color when the chemical reaction happens. Examples Ferroin changes from light blue to red. Starch iodide turns from blue to colorless.

12. Self Indicator The substance you are adding to the solution (titrant) changes the color itself when the reaction is complete. Examples: Potassium permanganate turns the solution pink. Iodine turns the solution brown.

13. External Indicator Instead of adding the indicator to the solution, you take a small sample out and test it with the indicator to see if the color changes. Example Potassium ferricyanide is used to check if a reaction is complete.

14. Instrumental Method Sometimes, instead of using color changes, special instruments like a potentiometer or conductometer are used to find out when the reaction is complete. Example Potentiometry helps detect the endpoint electronically.

15. Types of Redox Titration

16. Iodimetry Iodimetry is a type of redox titration that involves direct titration with iodine (I₂). It is based on the reaction where iodine is converted into iodide ions (I⁻). Iodine (I₂) acts as an oxidizing agent sodium thiosulphate ( Na₂S₂O ₃) mixed with potassium iodide (KI), water is added to make up the volume . Starch is added as an indicator I₂-starch complex = blue color All iodine has reacted, the solution becomes colorless Reaction: I₂ + 2Na₂S₂O₃ → 2NaI + Na₂S₄O ₆

17. Principle Iodine (I₂) acts as an oxidizing agent in this titration. A standard iodine solution is used to determine the concentration of reducing agents such as sodium thiosulphate (Na₂S₂O₃), arsenious acid (H₃AsO₃), etc. The endpoint is identified by using starch as an indicator , where the solution changes color from blue to colorless.

18. How it Works Iodine Solution: You take iodine (I₂) in a flask and mix it with potassium iodide (KI) and water. Starch Indicator: Add starch to this solution, which will turn the solution blue when iodine is present. Titration: Now, you slowly add sodium thiosulphate (a reducing agent) from a burette to the solution. Color Change: As sodium thiosulphate reacts with iodine, the blue color starts disappearing. When all the iodine has reacted, the solution becomes colorless. The blue color means iodine is still present. When the color disappears (turns colorless), it shows all the iodine has reacted, and this is the endpoint. Example Reaction: I₂ + 2Na₂S₂O₃ → 2NaI + Na₂S₄O₆ This means iodine (I₂) reacts with sodium thiosulphate to form sodium iodide ( NaI ).

19. Iodometry Iodometry is a type of indirect redox titration that involves the titration with iodine (I₂). It is based on the conversion of iodide (I⁻) to iodine (I₂), which is then titrated. Potassium iodide (KI) MnO ₂ is added forms iodine (I₂) Add some starch The Iodine is Blue with Starch sodium thiosulphate (Na₂S₂O₃) chemical reacts with iodine (I₂) and turns it into iodide (I⁻), which is colorless . 2KI+MnO2​+3H2​SO4​→I2​+2KHSO4​+MnSO4​+2H2​O

20. Principle In iodometry, a standard solution of sodium thiosulphate (Na₂S₂O₃) is used to titrate and measure the amount of iodine liberated from potassium iodide (KI) . This liberated iodine forms a complex with starch , creating a blue color, which helps indicate the endpoint of the titration.

21. Procedure Potassium iodide (KI) is taken in excess in a flask. An oxidizing agent (like MnO ₂) is added, which reacts with KI in the presence of an acidic medium (like H₂SO₄), liberating iodine (I₂). Reaction 2KI+MnO2​+3H2​SO4​→I2​+2KHSO4​+MnSO4​+2H2​O Starch is added as an indicator, forming a blue complex with iodine (I₂). This iodine-starch complex is then titrated with sodium thiosulphate (Na₂S₂O₃), which reduces the iodine back to iodide (I⁻). As the iodine is consumed, the blue color fades, and when the blue color completely disappears, it indicates the end point of the titration.

22. Applications Iodimetry It's used to measure the amount of sulfur dioxide and other reducing agents in a solution. Iodometry This method is used for the determination of both oxidizing and reducing agents due to its sensitivity in detecting iodine.

23. Cerimetry Titration Cerimetry is a specialized redox titration method utilizing cerium(IV) ions ( Ce⁴⁺ ) as a potent oxidizing agent . It involves the reduction of Ce⁴⁺ to Ce³⁺ by various reducing agents such as iodides , thiosulfates , and oxalic acid . Principle The titration is based on the redox reaction between the oxidizing agent ( Ce⁴⁺ ) and the reducing agent . At the equivalence point , the number of electrons transferred matches stoichiometrically. Cerium(IV) is yellow and serves as the indicator . Reduction to cerium(III) results in a colorless solution, signaling the endpoint . Key Reaction Ce 4 + + e − →Ce 3+

24. Cerimetry Titration Ce4 + +Fe2 + →Ce3 + +Fe 3+ Ceric ion+ Ferric ion→ Cerrium ion+ Ferrous ion yellow → colourless soln Fe 3+ <- Fe2 + Ce3 + (NH₄)₄Ce(SO₄)₄·2H₂O Cerric Ammonium sulphate → Ce4 + Cerric ion

25. Applications of Cerimetry Pharmaceutical Analysis : Used to determine ascorbic acid (Vitamin C) and hydrogen peroxide in formulations. Industrial Testing : Measures ferrous ions (Fe²⁺) and oxalates in chemical and metallurgical products. Environmental Monitoring : Used in the estimation of chemical oxygen demand (COD) in water and wastewater analysis. Food Industry : Quantifies antioxidants like Vitamin C in food samples. Academic Research : Demonstrates redox titration principles and studies reaction kinetics in laboratories.

26. Dichromate Titration

27. Dichromate Titration K2|Cr2O7  +Fe2 + →Ce3 + +Fe 3+ Potassium Dichromate+ Ferric ion→ Cerrium ion+ Ferrous ion Fe 3+ <- Fe2 + Ce3 + K2|Cr2O7 cromate ion /on=6 Cr +6 →

28. Bromatometry