Redox Titration

Redox titration can be based on an oxidation- reduction reaction between the titrant and the analyte. The concentration of unknown analytes can be determined through titration and it is considered as one of the most common laboratory methods of all time. The shape of the corresponding titration curve can be obtained by evaluating redox titrations. In this kind of titration, the monitoring of the concentration of a reacting species is monitored and proves very convenient than monitoring the reaction potential. Redox titration has both oxidation and reduction. The key features of the reduction reaction are as follows!

Reduction

Any substance which can undergo reduction can occur via :

• Addition of hydrogen.
• Oxygen removal from the substance.
• The electrons are accepted.
• Their overall reduction of the oxidation state occurs.

Oxidation

Any substance which can undergo oxidation can occur :

• When oxygen is added.
• The hydrogen is removed when it is attached to the species.
• When there is a loss/donation of electrons.
• When there is an increase in the oxidation state which is exhibited by the substance.

Therefore, we can understand that redox titrations involve an exchange of electrons in between the given analyte and the titrant. For example, the treatment of an iodine solution with an reducing agent involves the titration where the and point is determined with the help of a starch indicator. Here, the diatomic iodine is reduced to iodine ions (I^-), and the solution loses its blue color. This kind of titration is basically coined as iodometric titration.

Redox Titration Examples 

A very common example of redox titration is potassium permanganate (KMnO4) against oxalic acid. Let us discuss the process of this redox titration in detail. 

How to do Redox Titration?

Check out how to do redox titration!

Firstly, about 250 ml of the standard oxalic acid solution is prepared and the molecular mass of oxalic acid is determined by calculating the atomic mass of its constituent atom and the molecular mass H2O4.2H2O is calculated as 126. As the weight of oxalic acid which is required to make the 1000ml of 1M solution is 126g, the weight of oxalic acid needed to make 250ml of 0.1 M solution would be 126/ 1000 x 250 x 0.1 = 3.15g. 

Checking The Strength Of KMnO4Utilizing Oxalic Acid Solution

The analyte is oxalic acid and the titrant would be potassium permanganate in this titration. Hence, the oxalic acid acts as a reducing agent and the potassium permanganate acts as oxidizing agent. As the reaction is taking place in an acidic medium, the oxidizing power of permanganate ion would be increased and this acidic medium is curated by the addition of dilute sulphuric acid. 

MnO4-+8H++5e–→Mn2++4H2O

Here, the potassium permanganate acts as an indicator where the permanganate ions are deep purple. In this redox titration  where the MnO4  is being reduced to colourless manganese ions (Mn2+) in this acidic medium, the last drop of permanganate gives it a very light pink colour which reaches an endpoint. The chemical reaction can be represented in the following way- 

2KMnO4+3H2SO4→K2SO4+2MnSO4+3H2O+5[O]H2C2O4.2H2O+[O]→2CO2+3[H2O]×5

Complete Reaction

2KMnO4+3H2SO4+5H2O4.2H2O→K2SO4+2MnSO4+18H2O+10CO2

Ionic equation

MnO4-+8H++5e–→Mn2++4H2O]×2

C2O42-→2CO2+2e–]×5

Conclusion

Hence, redox titration is the method of determining the concentration of a given analyte which causes a redox reaction between the titrant and the analyte which is a laboratory process and such titrations are being done with the help of potentiometer or a redox indicator. These reactions are being used to determine the concentration of unknown analytes and it’s considered to be one of the most common laboratory methods in Chemistry.  The key features of redox titrations are as follows – reduction and oxidation.Reduction can occur when addition of hydrogen, removal of oxygen from the substance and acceptance of electrons whereas oxidation occurs when oxygen is added and hydrogen is removed which was attached to the species and there is a loss or donation of electrons from the substance.