Redox Titration - Definition, Examples, Types, Principle, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 05:05 PM IST

What is Redox Titration?

Redox Titration is a analytical method to determine the concentration of a provided analyte by triggering a redox reaction between the titrant and provided analyte of unknown strength. These types of titrations sometimes require the use of a potentiometer or a redox indicator.

Redox titration is based on an oxidation-reduction reaction between the titrant and the analyte. It is one of the most common laboratory methods to identify the concentration of unknown analytes.

In order to evaluate redox titrations, the shape of the corresponding titration curve must be obtained. In these types of titration, it proves convenient to monitor the reaction potential instead of monitoring the concentration of a reacting species.

As discussed earlier, redox reactions involve both oxidation and reduction. The key features of reduction and oxidation are discussed below.

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Reduction

A substance can undergo reduction can occur via:

The addition of hydrogen.
The removal of oxygen.
The acceptance of electrons.
A reduction in the overall oxidation state.

Oxidation

The following points describe a substance that has undergone oxidation.

The addition of oxygen.
Removal of hydrogen which was attached to the species.
The donation/loss of electrons.
An increase in the oxidation state exhibited by the substance.

Thus, it can be understood that redox titrations involve a transfer of electrons between the given analyte and the titrant.

Example of redox titration: Reacting iodine solution with any reducing agent. In this titration starch is used as an indicator.

Redox titration principle

The redox reaction is defined as the reaction between oxidizing agent and reducing agent. The redox reaction is also known as oxidation-reduction reaction. During the chemical reaction, the electrons is transferred to the reacting ions of the aqueous solution.

Redox titration curve

To determine the redox titration value, the shape of the titration curve is evaluated. The titration curve helps is determine the hydronium ion concentration (H₃O⁺ ) when the titrant is added.

Redox titration

Indicators

The redox indicator undergoes a colour change at specific electrode potential when added to the solution.

To undergo fast and reversible colour change, the equilibrium in the redox titration needs to be established quickly.

Common indicators of redox indicators:

phenanthroline metal complex and bipyridine metal complex. Here, the metal changes oxidation state.
Methylene blue.
The organic compounds are the most common redox indicator.
2,2'- Bipyridine

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redox indicators examples

pH dependent

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pH independent

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Redox titration

Redox reaction as the basis for titration

In redox titrations, oxidation-reduction reaction take place. In this reaction redox sensitive indicators are used to determine the strength of oxidant or reductant.

In this reaction oxidising agents like potassium permanganate, potassium dichromate and iodine are used.

Determining the Strength of KMnO₄ using Standard Oxalic Acid Solution

In the titration, the analyte used is oxalic acid and the titrant used is potassium permanganate. The oxalic acid acts as a reducing agent, and the KMnO₄ acts as an oxidizing agent. Since the reaction takes place in an acidic medium, the oxidizing power of the permanganate ion is increased. This acidic medium is created by the addition of dilute sulfuric acid.

MnO⁻⁴+8H⁺+5e−→Mn²⁺+4H₂O

Molecular equation

Molecular equation

Related Topics Link,

Complete Reaction

Complete Reaction

KMnO₄ is used as an indicator where the permanganate ions are a deep purple colour. In this redox titration, MnO^4– is reduced to colourless manganous ions (Mn²⁺) in the acidic medium. The last drop of permanganate gives a light pink colour which shows that the endpoint is reached. The following chemical equation can represent the reaction that occurs.

Potassium permanganate is a dark purple coloured liquids which is a strong oxidising agent. In these titration indicators are not utilised as potassium permanganate acts as a self indicator.

potassium permanganate acts as a self indicator

During the titration, the pink colour of potassium permanganate is discharged till the reductant is oxidised. As the solution gives tinge pink colour with the addition of single drp of potassium permanganate, the end point of titration is indicated.

potassium permanganate discharged reductant

The redox reaction where the oxidising agent does not act as the self-indicator, diphenym amine or N-phenylanthranilic acid is used.

In iodimetric titrations, iodine is directly titrated against a reducing agent.

Ex: In determining the hypo (or) sodium thiosulphate, iodine directly reacts with sodium thiosulphate. Here, starch is used as an indicator and produces an intense blue colour.

In Iodimetric titration, addition of an oxidising agent to excess iodide ions to produce iodine takes place which is then titrated with standard thiosulphate solution.

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Redox Titration Example

An example of a redox titration is the titration of potassium permanganate (KMnO₄) against oxalic acid (C₂H₂O₄). The procedure and details of this titration are discussed below.

Titration of Potassium Permanganate against Oxalic Acid

Prepare a standard Oxalic acid solution of about 250 ml.
The molecular mass of oxalic acid is calculated by adding the atomic mass of each constituent atom
The H₂C₂O₄.2H₂O molecular mass is 126
The weight of oxalic acid needed to prepare 1000 ml of 1M solution is 126 g. Hence, the weight of oxalic acid needed to prepare 250 ml of 0.1 M solution is

126/1000 x 250 x 0.1 = 3.15 g

Types of redox titration (redox titration types)

In Bromometry, bromine (Br₂) titrant is used.
In Cerimetry, cerium (IV) salts is used.
In Dichrometry potassium dichromate is used.
In Iodometry, iodine (I₂) is used.
Permanganometric titration uses potassium permanganate.

Application of redox titration

Redox titration is applied to analyse inorganic analytes. A redox titration is helpful in determining the concentration of unknown analyte using a standard titrant.
It is also utilised to analysis of organic analytes.
It is used in the industrial production of cleaning products. Nitric acid is formed from the oxidation reaction of ammonia. Redox reactions are also applied in the process of electroplating.

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NCERT Chemistry Notes:

Frequently Asked Questions (FAQs)

1. Which reducing agents used in volumetric analysis?

The common reducing agents that are used in redox titrations are - Fe²⁺, S₂O₃²⁻, MnO₄⁻, Vitamin C or ascorbic acid, Benedict's reagents to reduce cupric ions to form cuprous ions, manganese (II) sulfate to reduce oxygen in the water, etc

2. Define titrant

Titrant is a substance (such as a reagent solution of precisely known concentration) that is added in titration.

3. Give two example of indicators.

Phenanthroline , starch

4. Give one application of redox titration.

It is used to determine the concentration of unknown analyte.

5. Give two types of redox titration.

Bromometry, iodometry

6. Why is an indicator used in redox titration?

An indicator is used to visually signal the endpoint of the titration. It changes color when the reaction is complete, indicating that the analyte has fully reacted with the titrant.

7. What is a self-indicator in redox titration?

A self-indicator is a substance that acts as its own indicator during a redox titration. It changes color as it is oxidized or reduced, eliminating the need for an additional indicator.

8. How does potassium permanganate act as a self-indicator?

Potassium permanganate acts as a self-indicator because it changes from purple to colorless when reduced. The persistence of a faint pink color indicates the endpoint of the titration.

9. Why is standardization important in redox titration?

Standardization ensures the exact concentration of the titrant is known, which is crucial for accurate quantitative analysis. It compensates for any degradation or impurities in the titrant solution.

10. What is the difference between a primary standard and a secondary standard in redox titration?

A primary standard is a pure substance used to standardize a solution directly, while a secondary standard is a solution standardized against a primary standard. Primary standards are more reliable but may be less convenient to use.

11. What is the principle behind redox titration?

The principle of redox titration is based on the transfer of electrons between the analyte and titrant. The endpoint is reached when the number of electrons transferred from the reducing agent equals the number accepted by the oxidizing agent.

12. How does redox titration differ from acid-base titration?

Redox titration involves the transfer of electrons between species, while acid-base titration involves the transfer of protons. Redox reactions change oxidation states, whereas acid-base reactions change pH.

13. What is meant by the term "equivalence point" in redox titration?

The equivalence point is the theoretical point in a titration where the amount of titrant added is chemically equivalent to the amount of analyte present. At this point, the reaction between the analyte and titrant is complete.

14. How does the endpoint differ from the equivalence point?

The endpoint is the point at which a physical change (usually a color change) is observed, indicating the completion of the titration. The equivalence point is the theoretical point of complete reaction. Ideally, these points should coincide, but in practice, there may be a slight difference.

15. What is a redox indicator?

A redox indicator is a substance that changes color at a specific electrode potential. It is used to visually signal the endpoint of a redox titration by changing color when the reaction is complete.

16. What is redox titration?

Redox titration is an analytical technique used to determine the concentration of an oxidizing or reducing agent in a solution. It involves the transfer of electrons between the analyte and titrant, resulting in a change in oxidation states.

17. What is the role of a mediator in redox titration?

A mediator is a substance that facilitates electron transfer between the analyte and titrant in redox titrations. It can speed up slow reactions or enable reactions between species that wouldn't normally react directly.

18. Why is iodometry a widely used redox titration method?

Iodometry is widely used because iodine has a distinct color, making the endpoint easy to detect. It also forms a sensitive complex with starch, providing a sharp color change at the endpoint. Additionally, iodine can react with many reducing agents, making it versatile.

19. What is the difference between direct and indirect redox titration?

In direct redox titration, the analyte reacts directly with the titrant. In indirect redox titration, the analyte reacts with an excess of a reagent, and the unused reagent is then titrated. Indirect methods are useful when direct reactions are too slow or unreliable.

20. How does the concentration of reactants affect the accuracy of redox titration?

The concentration of reactants can affect reaction rates and equilibrium positions. Very dilute solutions may lead to indistinct endpoints, while very concentrated solutions might cause side reactions or rapid color changes that are difficult to observe accurately.

21. How does temperature affect redox titrations?

Temperature can affect the rate of reaction, the stability of reagents, and the color change of indicators in redox titrations. Higher temperatures generally increase reaction rates but may also lead to side reactions or decomposition of unstable compounds.

22. What is meant by a "blank titration" in redox analysis?

A blank titration is performed using all reagents except the analyte. It helps to account for any impurities or side reactions that might consume the titrant, allowing for more accurate results by subtracting the blank value from the actual titration.

23. Why is it important to use a burette in redox titration?

A burette allows for precise control and measurement of the volume of titrant added. This precision is crucial for accurate determination of the analyte concentration, especially when dealing with small volumes or dilute solutions.

24. How does the choice of indicator affect the accuracy of a redox titration?

The choice of indicator can affect accuracy if its color change doesn't coincide exactly with the equivalence point. Some indicators may change color slightly before or after the true endpoint, introducing systematic errors in the titration results.

25. What is potentiometric titration in redox analysis?

Potentiometric titration involves measuring the electrical potential difference between two electrodes as the titrant is added. It provides a more precise endpoint determination than visual indicators, especially for colored or turbid solutions.

26. How does complexation affect redox titrations?

Complexation can interfere with redox titrations by altering the availability of ions for oxidation or reduction. It can change the standard reduction potentials of species involved, potentially leading to unexpected results or incomplete reactions.

27. What is the significance of the Nernst equation in redox titrations?

The Nernst equation relates the electrode potential of a redox reaction to the concentrations of the oxidized and reduced species. It helps predict the direction of electron flow and the feasibility of redox reactions, which is crucial for designing and interpreting redox titrations.

28. How do you choose an appropriate titrant for a redox titration?

The choice of titrant depends on factors such as the nature of the analyte, the desired reaction rate, stability, ease of standardization, and the availability of suitable indicators. The titrant should react completely and rapidly with the analyte and have a well-defined stoichiometry.

29. What is meant by "back titration" in redox analysis?

Back titration involves adding an excess of a standard reagent to the analyte, then titrating the unreacted excess with a second standard solution. This method is useful when the analyte reacts slowly or incompletely with the titrant, or when it's difficult to determine the endpoint directly.

30. How does pH affect redox titrations?

pH can significantly affect redox titrations by altering the oxidation states of species involved, changing reaction rates, or affecting the stability of reagents. Some redox reactions are pH-dependent, and controlling pH is often crucial for accurate results.

31. What is the role of masking agents in redox titrations?

Masking agents are used to selectively bind or complex interfering substances, preventing them from participating in the redox reaction. This allows for the determination of a specific analyte in the presence of potentially interfering species.

32. How do you determine the feasibility of a redox titration?

The feasibility of a redox titration is determined by comparing the standard reduction potentials of the species involved. The reaction will proceed spontaneously if the overall cell potential is positive. Additionally, reaction kinetics, stability of reagents, and availability of suitable indicators are considered.

33. What is meant by "over-titration" in redox analysis?

Over-titration occurs when excess titrant is added beyond the equivalence point. This can lead to inaccurate results and is often indicated by a sudden change in the rate of color change or potential difference near the endpoint.

34. How does the presence of dissolved oxygen affect redox titrations?

Dissolved oxygen can act as an oxidizing agent, potentially interfering with redox titrations involving reducing agents. It may cause the titrant to be consumed by side reactions, leading to inaccurate results. Degassing solutions or using inert atmospheres can mitigate this issue.

35. What is the importance of standardization in iodometric titrations?

Standardization is crucial in iodometric titrations because iodine solutions are volatile and can change concentration over time. Regular standardization against a primary standard ensures accurate concentration determination and reliable analytical results.

36. How does the concept of formal potential differ from standard reduction potential in redox titrations?

Formal potential takes into account the effects of solution conditions (like pH, ionic strength, and complexation) on the redox behavior of a species, while standard reduction potential is measured under standard conditions. Formal potentials are often more relevant in practical redox titrations.

37. What is the role of supporting electrolytes in redox titrations?

Supporting electrolytes maintain a constant ionic strength in the solution, minimizing changes in activity coefficients during the titration. This helps ensure consistent behavior of the redox species and can improve the sharpness of the endpoint.

38. How do you account for side reactions in redox titrations?

Side reactions can be accounted for by using selective reagents, controlling reaction conditions (like pH or temperature), employing masking agents, or using indirect titration methods. Understanding the chemistry of all species present is crucial for identifying and mitigating side reactions.

39. What is the significance of the titration curve in redox analysis?

The titration curve, typically plotting potential against volume of titrant added, provides visual representation of the titration progress. It helps in identifying the equivalence point, assessing the sharpness of the endpoint, and understanding the overall behavior of the redox system.

40. How does the kinetics of electron transfer affect redox titrations?

The rate of electron transfer can significantly impact the practicality and accuracy of redox titrations. Slow electron transfer kinetics may lead to delayed endpoints or incomplete reactions, necessitating the use of catalysts, elevated temperatures, or alternative titration methods.

41. What is the difference between a reversible and irreversible redox reaction in titration context?

In a reversible redox reaction, the electron transfer can occur in both directions, allowing the system to reach equilibrium. Irreversible reactions proceed predominantly in one direction. Reversible reactions often provide sharper endpoints and are generally preferred in redox titrations.

42. How do you choose between visual and instrumental endpoint detection in redox titrations?

The choice depends on factors such as the color and clarity of the solution, the sharpness of the endpoint, required precision, and available equipment. Instrumental methods (like potentiometric titration) are often preferred for higher precision or when visual detection is challenging.

43. What is the role of oxidation numbers in understanding redox titrations?

Oxidation numbers help track the transfer of electrons in redox reactions. They are crucial for balancing redox equations, determining the equivalence point, and understanding the stoichiometry of the reaction, which is essential for accurate concentration calculations.

44. How does the concept of half-reactions apply to redox titrations?

Half-reactions represent the separate oxidation and reduction processes occurring in a redox reaction. Understanding half-reactions helps in balancing redox equations, predicting reaction spontaneity, and selecting appropriate titrants and indicators.

45. What are the challenges in performing redox titrations with colored solutions?

Colored solutions can mask the color change of indicators, making visual endpoint detection difficult. This challenge can be addressed by using instrumental methods, selecting indicators with color changes distinct from the solution color, or employing indirect titration techniques.

46. How does the presence of complexing agents affect redox potentials in titrations?

Complexing agents can alter the effective concentration of redox-active species, changing their apparent redox potentials. This can affect the position of the equivalence point and the overall titration behavior, necessitating careful consideration of solution chemistry.

47. What is the importance of stoichiometry in redox titrations?

Stoichiometry is crucial for relating the amount of titrant consumed to the amount of analyte present. Accurate knowledge of the reaction stoichiometry is essential for calculating concentrations and ensuring the validity of the titration method.

48. How do you handle redox titrations involving multiple analytes?

Titrations involving multiple analytes may require selective oxidation or reduction, stepwise titration procedures, or the use of masking agents to analyze each species separately. Careful control of reaction conditions and selection of appropriate titrants are essential.

49. What is the role of electrochemistry in understanding redox titrations?

Electrochemistry provides the theoretical foundation for redox reactions, helping to predict reaction spontaneity, calculate equilibrium constants, and understand the behavior of redox indicators. It's crucial for designing effective titration methods and interpreting results.

50. How does the concentration of the titrant affect the precision of a redox titration?

The concentration of the titrant affects the volume needed to reach the endpoint. More concentrated titrants require smaller volumes, potentially increasing precision but also increasing the risk of overshooting the endpoint. The optimal concentration balances these factors and depends on the specific analysis.

51. What are the advantages and limitations of using cerium(IV) as a titrant in redox titrations?

Cerium(IV) is a strong oxidizing agent, making it useful for many redox titrations. Advantages include its high oxidation potential and stability. Limitations include its sensitivity to light, potential for hydrolysis in aqueous solutions, and the need for acidic conditions to prevent precipitation.

52. How do you account for the uncertainty in the endpoint determination of a redox titration?

Uncertainty in endpoint determination can be minimized by using precise volumetric glassware, repeating titrations, employing statistical analysis, and using instrumental methods for endpoint detection. The uncertainty should be reported along with the final result.

53. What is the significance of the formal potential in designing redox titrations?

The formal potential, which accounts for actual solution conditions, is more relevant than standard potentials for predicting the behavior of redox systems in real titrations. It helps in selecting appropriate titrants, indicators, and reaction conditions for effective analyses.

54. How does the presence of catalysts affect redox titrations?

Catalysts can accelerate slow redox reactions, improving the sharpness of endpoints and reducing titration time. However, they must be carefully chosen to avoid interfering with the main reaction or introducing additional uncertainties in the analysis.

55. What are the key considerations in validating a new redox titration method?

Validating a new redox titration method involves assessing accuracy, precision, linearity, range, selectivity, and robustness. This includes analyzing standard samples, comparing results with established methods, evaluating potential interferences, and determining method limitations and uncertainties.