NEET Notes: Redox Reactions

Introduction

Redox reactions, also known as oxidation-reduction reactions, are fundamental chemical processes where the transfer of electrons occurs between two substances. These reactions are crucial in various biological, industrial, and environmental processes, including respiration, combustion, corrosion, and electrochemistry. Understanding redox reactions is essential for NEET aspirants as they form the basis of many chemical concepts.

Oxidation and Reduction

1. Definition of Oxidation

Oxidation is the process in which a substance loses electrons. It often involves the addition of oxygen or the removal of hydrogen in a reaction.

2. Definition of Reduction

Reduction is the process in which a substance gains electrons. It generally involves the removal of oxygen or the addition of hydrogen.

3. Simultaneous Nature of Oxidation and Reduction

Oxidation and reduction always occur together in a redox reaction. When one substance loses electrons (oxidation), another substance gains those electrons (reduction).

Oxidizing and Reducing Agents

1. Oxidizing Agent

An oxidizing agent (oxidant) is a substance that gains electrons and undergoes reduction. It helps in oxidizing other substances by accepting their electrons.

2. Reducing Agent

A reducing agent (reductant) is a substance that donates electrons and undergoes oxidation. It helps in reducing other substances by providing electrons.

3. Examples of Oxidizing and Reducing Agents

• Oxidizing Agents: Oxygen, chlorine, nitric acid, hydrogen peroxide, potassium permanganate.

• Reducing Agents: Hydrogen, carbon, sodium, zinc, iron, sulfur dioxide.

Types of Redox Reactions

1. Combination Reactions

In a combination reaction, two or more reactants combine to form a single product. If electron transfer occurs, it is considered a redox reaction.

2. Decomposition Reactions

In a decomposition reaction, a single compound breaks down into two or more products. If this process involves electron transfer, it qualifies as a redox reaction.

3. Displacement Reactions

A displacement reaction occurs when a more reactive element replaces a less reactive element in a compound. These reactions usually involve metals and are commonly seen in electrochemical reactions.

4. Disproportionation Reactions

A disproportionation reaction is a special type of redox reaction in which the same element undergoes both oxidation and reduction.

Oxidation Number and Its Significance

1. Definition of Oxidation Number

The oxidation number (oxidation state) is the charge an atom would have if electrons were completely transferred in a reaction. It helps in identifying oxidation and reduction in a chemical reaction.

2. Rules for Assigning Oxidation Numbers

• The oxidation number of an element in its pure form is always zero.

• The oxidation number of hydrogen is +1 (except in metal hydrides, where it is -1).

• The oxidation number of oxygen is usually -2 (except in peroxides, where it is -1).

• The sum of oxidation numbers in a neutral compound is zero.

3. Importance of Oxidation Numbers

• Helps in balancing redox reactions.

• Identifies oxidizing and reducing agents.

• Predicts the feasibility of a reaction.

Balancing Redox Reactions

1. Ion-Electron Method (Half-Reaction Method)

The ion-electron method is a systematic approach used to balance redox reactions by considering oxidation and reduction half-reactions separately.

2. Oxidation Number Method

In this method, oxidation numbers are assigned to elements in the reaction, and changes in oxidation states are used to balance the equation.

3. Steps to Balance a Redox Reaction

• Identify the oxidation and reduction half-reactions.

• Balance atoms other than hydrogen and oxygen.

• Balance oxygen atoms using water molecules.

• Balance hydrogen atoms using hydrogen ions (H⁺).

• Balance charges by adding electrons.

• Combine the balanced half-reactions.

Applications of Redox Reactions

1. Biological Processes

Redox reactions play a crucial role in metabolism, respiration, and photosynthesis. In cellular respiration, glucose is oxidized to release energy.

2. Industrial Applications

• Electrochemical Cells: Batteries and fuel cells operate based on redox reactions.

• Metallurgy: Extraction of metals from ores involves redox processes.

• Bleaching: Redox reactions help in the bleaching of fabrics and paper.

3. Environmental Impact

• Corrosion of Metals: Iron rusting is a redox reaction where iron reacts with oxygen and water.

• Water Purification: Redox reactions are used to remove contaminants from water.

Redox Reactions in Everyday Life

1. Rusting of Iron

Iron reacts with oxygen and moisture to form iron oxide (rust). This process is a redox reaction where iron is oxidized and oxygen is reduced.

2. Combustion Reactions

Burning of fuels like wood, coal, and petrol involves redox reactions, where carbon compounds are oxidized to produce energy.

3. Photosynthesis

In plants, redox reactions convert sunlight into chemical energy. Water is oxidized to release oxygen, while carbon dioxide is reduced to form glucose.

Conclusion

Redox reactions are fundamental to chemistry and play a significant role in biological, industrial, and environmental processes. Mastering the concepts of oxidation, reduction, oxidation numbers, and balancing techniques is essential for NEET aspirants. A clear understanding of redox reactions helps in solving problems related to electrochemistry, metabolism, corrosion, and energy production.