Redox Titration

Redox titration refers to a laboratory method to determine the analyte concentration by carrying out a redox reaction between the analyte and the titrant. The redox titration often needs a redox indicator or a potentiometer. Rodex titration depends on an oxidation-reduction reaction that occurs between the analyte and the titrant. It is also one of the most common methods for identifying the concentration of the analytes that are unknown. For evaluating the redox titrations, it is essential to obtain the shape of the titration curve that corresponds. In redox titration, it is much more convenient for monitoring the concentration of the reaction potential instead of that of the reacting species.

Principle of Redox Titration

Let us discuss the theory of redox titration. Redox reactions consist of both oxidation and reduction reactions. The primary features of these reactions are as follows:

1. Reduction Reaction

A substance undergoes a reduction in the following ways:

• Addition of hydrogen atom

• Removal of the oxygen atom

• Accepting electrons

• Reduction in the oxidation state of the substance

2. Oxidation Reaction

A substance undergoes oxidation in the following ways:

• Addition of oxygen

• Removal of hydrogen

• Loss or donation of electrons

• An overall increase in the oxidation state of the substance

Hence, we can say that redox titrations consist of a transfer of electrons between the titrant and the analyte. An example of this type of redox reaction is reacting the iodine solution with a reducing agent. A starch indicator is used to determine the endpoint of this redox titration. Here, the diatomic iodine gets reduced to the iodine ions and the blue coloured iodine solution loses its colour. This reaction is known as iodometric titration.

Redox Titration Examples

The titration of potassium permanganate against oxalic acid is a great example of redox titration. The reaction is explained below.

Example - Titration of Potassium Permanganate Against Oxalic Acid

1. Firstly prepare a standard oxalic acid solution, roughly 250 ml.

2. The molecular weight of oxalic acid can be calculated when the atomic weight of all the atoms is added.

Doing so, we get the molecular mass of oxalic acid, which is,

                                               H2C2O4.2H2O = 126

3. As the weight of the required oxalic acid for making 1000 ml of 1M solution is found to be 126g, the weight of the same for making 250ml of 0.1M solution is,

                                      = \[\frac{126}{1000}\] х 250 х 0.1 = 3.15g 

Redox Titration Indicators

There are three different types of indicators that are required for signalling the endpoint of redox titration. The oxidised and reduced forms of titrants like MnO₄^- possesses different colours. The MnO₄^- the solution is a strong purple colour, however, when it is used as a titrant, the mixture tends to remain colourless till the equivalence point is reached. The endpoint is indicated by the very first drop of the excessive MnO₄^- which gives the solution a permanent purple colour.

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Amongst the most vital class of indicators, lie these materials which do have a contribution in the redox titration, however, their oxidised and reduced forms are different in colour. When a redox indicator is added to the titrant, the colour imparted by the indicator is dependent on the potential of the solution. Since the potential of the mixture tends to change when the titrant is added, the indicator changes the oxidation state and the colour, which indicates the endpoint of the titration.

Conclusion

The article is very useful for the students because the concept of redox titration is used in chemistry many times. Hence students must have a clear understanding of this concept. The article discusses the principle, examples and redox titration indicators.