Redox reactions in titrations

What is titration?

A method for determining the amount of a substance ‘A’ by adding calibrated amounts of substance ‘B’ to which it will react until the equivalence point is reached.

What are redox reactions in titrations?

The redox titration is defined as follows: ‘A redox titration is one in which the analyte and the titrant undergo an oxidation–reduction reaction.’ The endpoint of a redox titration is frequently detected using an indicator, just as it is in acid–base titrations.

One of the most frequent laboratory methods for determining the number of the analytes present is chromatography.

The corresponding titration curve is also generally obtained to evaluate redox titrations. It is more convenient to measure the reaction potential rather than the concentration of a responding species in these types of titrations.

Principle of redox reactions in titrations

Let’s talk about the redox titration theory. Both oxidation and reduction reactions are included in redox reactions. The following are the main characteristics of these reactions:

Reaction to reduction

Material can be reduced in one of the following ways:

• By adding a hydrogen atom to the mix.
• By removing the oxygen atom from the compound.
• By accepting electrons
• By reducing the substance’s oxidation state

Reaction of oxidation

The following are examples of how a material can be oxidised:

• By supplementing oxygen to the material.
• By removing hydrogen atom
• By losing or donating electron
• By increasing the oxidation state of the substance as a whole.

As a result, redox titrations consist of an electron transfer between the titrant and the analyte. Reacting the iodine solution with a reducing substance is an example of this type of redox reaction. The endpoint of this redox titration is determined using a starch indicator.

Types of redox titration

Iodometric titration

Iodometric titration is a technique for detecting the concentration of an oxidising agent in a sample solution. It’s a sort of redox titration that titrates iodine using sodium thiosulphate as a reducing agent. Because it can absorb the iodine (I2) that is emitted, a starch solution is utilised as an indicator in an iodometric titration. This approach is used to directly titrate an analyte that is a reducing agent with a standard iodine solution.

Bromatometry titration

Bromatometry is a titration method that uses potassium bromate as an oxidant. It’s a form of redox titration that’s used to figure out how much a chemical indicator has brominated.

Titration using cerimetry

Cerimetry is a volumetric chemical analysis method that can be used to examine nonstoichiometric levels that oxidise or decrease Fe3+. A colour change in the iron (II), 10-phenanthroline complex determines the endpoint of this form of redox titration (ferroin).

Permanganometric titration

This is a sort of redox titration in which the amount of analyte contained in an unknown sample solution is determined using permanganate. Manganese (II), iron (II), oxalate, nitrate, and hydrogen peroxide, among other chemical species, can be detected and quantified using permanganometry.

Dichrometry titration is a type of qualitative chemical analysis that involves the use of potassium dichromate (K2Cr2O7) to determine the amount of solute in a sample.

Redox titration example

The titration of potassium permanganate (KMnO4) against oxalic acid (H2C2O4) is a redox titration example. This titration’s technique and specifics are detailed further down.

Potassium permanganate titration against oxalic acid

Prepare a 250 ml solution of standard oxalic acid. The atomic mass of each constituent atom is added to get the molecular mass of oxalic acid. H2C2O4.2H2O has a molecular mass of 126.

Because the amount of oxalic acid needed to generate 1000 ml of 1M solution is 126 g. As a result, the amount of oxalic acid required to make 250 ml of 0.1 M solution is 126/1000 x 250 x 0.1 = 3.15 g.

Indicators of redox titration 

For signalling the endpoint of redox titration, three different types of indicators are necessary. Titrants like MnO4- have various colours in their oxidised and reduced states. The solution of MnO4- is a deep purple colour, but when used as a titrant, the combination tends to remain colourless until the equivalence point is achieved. The endpoint is marked by the first drop of extra MnO4- in the solution, which turns it permanently purple.

These materials, which contribute to redox titration yet have various colours in their oxidised and reduced forms, are among the most important class of indicators. When a redox indicator is added to the titrant, the colour the indicator imparts is determined by the solution’s potential. The indicator affects the oxidation because the mixture’s potential changes when the titrant is applied.

Advantages and disadvantages of redox titration:

The benefits of redox titration include:

• It’s usually inexpensive, and it just necessitates a few pieces of equipment that are commonly found in labs.
• It does not necessitate the use of any special or costly chemicals.
• It does not necessitate a high level of knowledge and has a simple operating method.
• The analysis may be automated, and the results are extremely precise.
• Provides immediate results.

Redox titration has several disadvantages. Some of them are as follows:

• It’s a destructive approach that typically consumes a lot of the item being studied.
• It necessitates the occurrence of reactions in a liquid state.
• It generates a lot of chemical waste.

Conclusion

The redox reactions in titration are an important topic and are a part of redox reactions in chemistry. A redox reaction between the titrant and the analyte is employed in a laboratory environment to determine the concentration of a specific analyte. These types of titrations may necessitate the use of a potentiometer or a redox indicator.