Oxidation-Reduction Titrations

What is Oxidation-Reduction Titration?

Oxidation-Reduction titration or Redox titration is a laboratory procedure for determining an analyte’s concentration. It involves the use of a potentiometer which is completely based on a redox reaction.

Redox reactions can be found everywhere. In reality, redox processes underpin most of our technology, from fire to laptop batteries. Redox reactions can be simple, such as the combustion of carbon in oxygen to produce carbon dioxide, or more complex, such as the oxidation of glucose in the human body through a variety of electron transfer mechanisms.

Redox titrations, as we know, are based on redox reactions, which are essentially the oxidation-reduction reactions.

Examples of Redox Titration

1. The most frequent example of redox titration is when we use a starch indicator to detect the endpoint after treating an iodine solution with a reducing agent like thiosulfate to make iodide. Iodometric titration is another name for this. 
2. Oxalic acid titration of potassium permanganate is another example.

How will we get to know that a Substance has Undergone Reduction?

If even one of the four choices below is true, then we can say that material has been reduced:

1. If the substance gains electrons.
2. If the substance contains hydrogen.
3. If the provided substance is depleted of oxygen.
4. If the substance’s oxidation state decreases.

As a result, we conclude that there is an electron transfer between the analyte and the titrant in redox titrations.

How do you carry out a Redox Titration?

A permanganate titrant’s concentration can be standardised by reacting it with a precise amount of high-purity material. Oxalic acid is frequently used for this purpose.

Q: Look at the reactions below to see how thiosulphate reacts with both bromine and iodine in different ways.

2 S₂O₃^2– + I₂ → S₄O₆^2– + 2I–

S₂O₃^2–+ 2Br₂  + 5H₂ O → 2SO_4^2–  + 2Br– + 10 H+

Choose the statement that best explains the thiosulphate’s dual behaviour in the above reactions.

• Iodine has a higher oxidant strength than bromine.
• Bromine has higher oxidising power than iodine.
• Iodine and bromine undergo reduction and oxidation, respectively.
• Thiosulphate is reduced and oxidised by bromine and iodine, respectively.

Bromine is a more powerful oxidizer than iodine. In comparison to iodine, bromine is a more powerful oxidizer. Therefore, bromine oxidises S of S₂O₃^2– to 2SO_4^2– whereas I₂ oxidises S to S₄O_6^2– . Once you are done with the estimation, you will find that the oxidation number of S₄O_6^2– is less than 2SO4^2– .

What are the indicators used in Oxidation-Reduction Titration?

Colorimetric reagents that show a particular colour shift at a specific electrode potential are known as oxidation/reduction (redox) indicators. These are all reversible redox reactions in organic molecules. M-cresol-indophenol, Anilinic acid, eriogreen, diphenylamine, methylene blue, and Nile blue are among the examples.

• A redox indicator is a molecule that changes colour when potential differences are changed.
• The reduced and oxidised forms of a redox indicator molecule must exhibit different hues, and the redox process must be reversible. Furthermore, the oxidation-reduction equilibrium must be swiftly achieved. Redox indicators are only suitable for a few types of compounds:
• Metal complexes of phenanthroline and bipyridine: The metallorganic systems change colour as the oxidation state of metal varies.
• Organic redox compounds: A proton participates in the redox reaction in these indicators. Methylene blue is an example of this type of indicator.

Examples of Redox Indicators

2,2′-Bipyridine is a redox indicator chemical. At an electrode potential of 0.97 V, it transforms from light blue to red in solution.

Conclusion

Redox titration is a scientific procedure that uses a redox reaction between the analyte and the titrant to estimate the analyte concentration. A redox indicator or a potentiometer is frequently required for redox titration. The analyte and the titrant undergo an oxidation-reduction reaction, which is used in redox titration. It’s also one of the most used procedures for determining the concentration of unknown analytes. It is critical to obtain the shape of the titration curve that matches when analysing redox titrations. In redox titration, monitoring the concentration of the reaction potential rather than the reacting species is significantly more convenient.