Redox titration is a method used to determine the concentration of a substance in a solution by measuring the volume or concentration of another substance that undergoes oxidation-reduction reactions with it.

In this article, we will understand the meaning of redox titration, the reduction and oxidation of redox titration, the principle of redox titration, indicators of redox titration and the molecular equation of redox titration.

What is Redox Titration?

Redox titration is a method used in labs to find much of a substance, called an analyte, is in a solution. It works by making a reaction between the analyte and another substance called a titrant. Sometimes, scientists use a potentiometer or a special chemical called a redox indicator to help with this process.

The process of redox titration relies on the oxidation-reduction reaction between the titrant and the analyte. It is widely used in laboratories to identify the concentration of unknown analytes.

To assess redox titrations accurately, it is necessary to obtain the shape of the corresponding titration curve. In these types of titrations, it is practical to monitor the reaction potential rather than monitoring the concentration of a reacting species.

Reduction

Reduction is a chemical process in which a substance gains electrons or decreases in oxidation state. It involves the addition of hydrogen or the removal of oxygen from a compound.

The primary features of redox titration during reduction reaction are as follows:

• Reduction involves the gain of electrons by a substance or a decrease in its oxidation state.
• In redox titration, reduction occurs when the analyte gains electrons from the titrant.
• This process often results in a change in color, formation of a precipitate, or release of gas, depending on the specific reaction.

Oxidation

Oxidation is a chemical process in which a substance loses electrons or increases in oxidation state. It involves the addition of oxygen or the removal of hydrogen from a compound.

The primary features of redox titration during oxidation reaction are as follows:

• Oxidation involves the loss of electrons by a substance or an increase in its oxidation state.
• In redox titration, oxidation occurs when the titrant loses electrons to the analyte.
• Similar to reduction, oxidation reactions in redox titration can lead to observable changes such as color changes, formation of precipitates, or release of gases.

Principle of Redox Titration

The principles of redox titration are:

• Oxidation-Reduction Reactions: Redox titrations involve reactions where one substance is oxidized (loses electrons) and another is reduced (gains electrons).
• Titration Endpoint: The endpoint is determined by a slight change in the system, like a color change or appearance of a precipitate, indicating that the reaction is complete.
• Equivalence Point: At this point, the amount of titrant added is equal to the amount of analyte present, marking the completion of the reaction.
• Titration Curves: These curves show pH or potential changes as titrant volume increases, reflecting the reaction’s progress.
• Choice of Indicator: Indicators are selected based on their ability to change color near the equivalence point.
• Stoichiometry: Balanced chemical equations help calculate the amount of titrant needed for the reaction.
• Standardization: Titrant solutions are standardized against known standards to ensure accuracy before use.

Redox Titration Indicators

In redox titrations, there are three types of indicators crucial for signaling the endpoint. The titrants, like MnO₄^–, have distinct colors in their oxidized and reduced forms. Although MnO₄^– solution appears as a strong purple color, during titration, the mixture remains colorless until the equivalence point. The endpoint is indicated by the first drop of excess MnO₄^–, which turns the solution permanently purple.

One essential class of indicators for redox titrations includes materials with different colors in their oxidized and reduced forms. When added to the titrant, these indicators change color based on the solution’s potential. As the titrant is added and the potential of the solution changes, the indicator’s oxidation state and color also change, marking the titration’s endpoint.

Redox Titration Example

A common example of redox titration involves the titration of potassium permanganate (KMnO₄) with oxalic acid (C₂H₂O₄). The steps and specifics of this titration are outlined below.

Titration of Potassium Permanganate against Oxalic Acid

To prepare a standard solution of oxalic acid with a volume of approximately 250 ml, one need to follow these steps:

• Determine the molecular mass of oxalic acid, which is calculated by adding the atomic mass of each constituent atom. The molecular mass of H₂C₂O₄⋅2H₂O is 126.
• Calculate the amount of oxalic acid needed to make a 0.1 M solution in 250 ml. Since the weight of oxalic acid required to prepare 1000 ml of a 1 M solution is 126 g, the weight needed for 250 ml of a 0.1 M solution is 126/1000×250×0.1 = 3.15.

Redox Titration Reaction

The reaction of Redox Titration is done as followed:

Step 1: Start by preparing a solution of oxalic acid in a flask. Measure out the calculated amount of oxalic acid and dissolve it in water to make the desired volume, approximately 250 ml.

Step 2: Add a suitable indicator to the oxalic acid solution. In this case, a suitable indicator could be a few drops of sulfuric acid.

Step 3: Using a burette, add a standardized solution of potassium permanganate (KMnO₄) to the oxalic acid solution. The potassium permanganate solution is slowly added to the oxalic acid solution while stirring continuously.

Step 4: The titration is complete when a permanent pink color appears in the solution. This color change indicates that all the oxalic acid has reacted with the potassium permanganate.

Step 5: From the volume of potassium permanganate solution used and its known concentration, the amount of oxalic acid in the sample can be calculated using the balanced chemical equation for the reaction between oxalic acid and potassium permanganate.

Molecular Equation of Redox Titration

The Molecular Equation of Redox Titrations is written as follows:

KMnO₄​ + FeSO₄​ + H₂​SO₄ ​→ MnSO₄​ + Fe₂​(SO₄​)₃​ + H₂​O

In this reaction, potassium permanganate (KMnO₄KMnO₄​) is the oxidizing agent, while ferrous sulfate (FeSO₄FeSO₄​) is the reducing agent. The potassium permanganate oxidizes the ferrous ions in the ferrous sulfate solution to ferric ions, while it itself undergoes reduction to manganese ions. The balanced equation shows the stoichiometry of the reaction between the titrant (potassium permanganate) and the analyte (ferrous sulfate) in the presence of sulfuric acid (H₂SO₄H₂​SO₄​).

Iconic Equation: 5C_2​O₄²⁻​+ 2MnO₄⁻​+ 16H⁺→10CO₂​ + 2Mn²⁺+ 8H₂​O

Complete Reaction: 5Na₂​C₂​O_4​ + 2KMnO₄​ + 8H₂​SO₄​ → 10CO₂​ + 2MnSO₄​ + 8H₂​O + 2K₂​SO₄​

Also, Check

• Applications of Titration
• Acid-Base Titration
• Difference Between Endpoint and Equivalence Point

Frequently Asked Questions on Redox Titration

What is meant by redox titration?

Redox titration is a chemical analysis technique used to determine the concentration of an analyte by measuring the volume or concentration of a titrant that reacts with it in a redox reaction. In redox titrations, the titrant and analyte undergo oxidation-reduction (redox) reactions, where one species loses electrons (oxidation) while the other gains electrons (reduction).

What is the redox titration equation example?

An example of a redox titration equation is the titration of potassium permanganate (KMnO₄) with sodium oxalate (Na₂C₂O₄), which can be represented as: 5Na₂C₂O₄+2KMnO₄+8H₂SO₄→10CO₂+2MnSO₄+8H₂O+2K₂SO₄

What is a redox acid base titration?

A redox acid-base titration combines the principles of redox titration and acid-base titration. In this type of titration, the analyte is a substance that can undergo both oxidation-reduction and acid-base reactions. The titration is typically carried out using a redox indicator or a pH indicator to detect the endpoint, where the equivalence point is reached when the moles of acid are equal to the moles of base or when the redox reaction is complete.

What is the end point in redox titration?

The endpoint in redox titration is the point in the titration where the reaction between the titrant and analyte is complete. It is signaled by a noticeable change in the system, such as a color change, formation of a precipitate, or a change in pH. The endpoint indicates that the stoichiometric amount of titrant has reacted with the analyte, and further addition of titrant does not cause any additional reaction.

What are the 4 types of titration?

The four main types of titration are acid-base titration, redox titration, complexometric titration, and precipitation titration. Each type of titration is used to determine the concentration of a specific analyte by reacting it with a known titrant under controlled conditions and observing a measurable change in the system.

What are the applications of redox titration?

Redox titration has various applications in analytical chemistry, including:

• Determination of the concentration of oxidizing or reducing agents in a sample.
• Analysis of transition metal ions in solution.
• Determination of the purity of pharmaceuticals and chemicals.
• Measurement of dissolved oxygen in environmental samples.
• Monitoring the progress of chemical reactions and processes in industries such as pharmaceuticals, food, and water treatment.