Here’s what you need to know about redox titration curve in potentiometry

Potentiometry is also known as Potentiometric titration. It is a technique used to characterize and measure the potential of an analyte. 4 different types of potentiometric titrations are known: acid-base titration, redox titration, complexometric titration, and precipitation titration. All 4 types of titration have their roles to play in analytical chemistry. Redox is a type of reaction where oxidation and reduction are carried out simultaneously in a single reaction. This property of chemical reactions is also used in the technique of potentiometry. The classic experiment performed using this technique is to calculate the strength of potassium

permanganate using an oxalic acid solution. This technique is also used in the pharmaceutical industry.

Potentiometry

Potentiometry, also known as potentiometric titration, is a technique used to determine the potential of an analyte. Also, the amount of analyte is determined by adding titrants of known concentration till the endpoint. Potentiometric titrations can be divided into 4 categories based on the type of reaction taking place.

• Acid-Base titration- this type of titration is used in potentiometry to calculate the concentration of an acid or a base using another base or acid respectively with a known concentration. Given we know that acid and a base neutralize each other.
• Complexometric titration- is also known as chelatometry, where the formation of a coloured complex marks the endpoint of the titration. It is used to determine the mixture of metal ions in a given solution.
• Precipitation titration- in this reaction, a precipitate is formed due to the reaction of an analyte and a titrant. When the precipitate formation stops even after the addition of titrant, then the titration is considered to reach its endpoint.
• Redox titration- here, the analyte and titrant perform the redox reaction.

Redox titration

It is a mechanism that determines the concentration of the analyte that undergoes redox reaction in the presence of the titrant. A potentiometer, which is the instrument used in potentiometry, is used to carry out the process of redox titration. Here the analyte and titrant react with each other through the redox reaction by carrying out oxidation and reduction. The results of a redox titration are incomplete without the redox titration curve. 

Redox titration example is the reaction between potassium permanganate and oxalic acid. Using this method, the strength of potassium permanganate can be calculated easily if the concentration of oxalic acid is known.

What is the redox titration curve?

The results of redox titration are evaluated easily through the redox titration curve. To understand the redox titration curve, let us consider an example.

Let us consider an analyte that is present in reduced state Xred and a titrant in oxidized state Yoxd. When these will combine, a titration reaction will occur. The chemical equation for this titration is as follows:

Xred + Yoxd ↔ Xoxd + Yred

It is the difference between the reduction potentials for both oxidation and reduction half of an electrochemical cell that determines the electrochemical potential of the reaction.

E= E(Yoxd/Yred) – E(Xoxd/Xred)

The reaction is always maintained at equilibrium; hence, the electrochemical potential is always zero for this reaction. Then the equation will be

E(Yoxd/Yred) = E(Xoxd/Xred)

The potential of either the oxidation half or the reduction half is used to monitor the progress of the titration process.

Further, the potential can be calculated using Nernst’s equation. After calculating the potential at various concentrations of the titrant, a graph can be plotted easily. In the graph, the volume of titrant in ml is plotted on the x-axis, and the potential in V is plotted on the y-axis. The curve obtained is a negative sigmoidal curve. From this curve, the potential of an unknown concentration of titrant can be calculated easily. Relation between the redox titration and the redox titration curve is that plotting the results of redox titration in the redox titration curve can be used to calculate the potential of a known concentration of titrant, and can also determine the concentration of an unknown titrant using its known potential value.

Conclusion

The Redox titration mechanism in potentiometry is a very useful tool of analytical chemistry that can help to calculate the potential as well as the concentration of a substance. Here, the properties of redox chemical reactions of different substances are used to reach the end goal of the experiment. This type of potentiometry is widely used in schools to teach students the basis of titration for their higher studies. The main application of redox titration is to measure the concentration of an unknown analyte against a known titrant. Apart from this, there are many real-life examples of this process like the electroplating mechanism, combustion mechanism, and many more. It also has a very important role to play in the pharmaceutical industry.