JEE Main Study Notes for Redox Reactions: Redox reaction is one of the types of chemical reaction. Redox reaction is the cause of the alternation in the oxidation states of atoms. Among different chemical species, there is the actual transfer or shifting of electrons takes place. In this reaction, one specie loses electrons and other species gains the electron.

Redox Reactions is one of the most important topics in Physical Chemistry of JEE Main Syllabus. JEE Main 2022 candidates can expect at least one question from the topic in the upcoming examination, concluding that the section has about 3.33% weightage in the paper. Since the topic is mainly equation-based only the objective type of questions will be framed in this section.

There is a list of subtopics that are covered under this section such as Balance Redox Reactions, Classical Idea of Redox Reactions, Oxidation Number, Redox Reactions and Electrode Potential, Types of Redox Reactions, Redox Reactions as the Basis of Titrations, Redox Reactions - Electron Transfer Reactions, etc. To know about tips and shortcuts to prepare them, read the article below. Check JEE Main Chemistry Syllabus

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What are Redox Reactions?

Redox Reaction is defined as a reaction mechanism in which the metal's oxidation state is replaced during the reaction. Based on the Reaction type, the state of oxidation can be increased or decreased.The most common example of redox reaction is the formation of the rust on a metal surface.

Speaking of applications of Redox Reactions, the major application of Redox mechanisms is in Electrochemical processes and Electrolysis. Basically, redox reactions define the concept of electrode and cell processes. SImilarly, redox reactions from a core concept of titration.

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Oxidation Numbers of Common Elements

In order to understand and solve redox reactions, oxidation numbers of common elements must be remembered, the table for which is given below.

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JEE Main Study Notes for Redox Reactions: Reactions Types

The several Redox Reactions are defined in the section below:

Combination Reactions

This reaction occurs in a situation when two or more than two substances are mixed up to form a substance. All the substances need to be in their elemental form.

Decomposition Reaction

This reaction is just opposite to the Combination Reaction. In this reaction, there are two or more than two substances formed as a result.

Displacement Reaction

In this reaction, a single ion of a compound is changed by an ion of another element.There are three types of displacement reaction such as metal displacement reaction, reactivity of non metals and non metal displacement reaction.

Disproportionation Reactions

It is such a reaction where the same element is oxidized and reduced simultaneously.

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Redox Reactions - Previous Years JEE Main Questions

1. In the section below, some questions from the previous year are mentioned.

XNa2HAsO3 +YNaBrO3+ZHCl → NaBr + H3AsO4 + NaCl

What are the values of X, Y and Z in the redox reaction mentioned above?

(1) 2, 1, 3

(2) 3, 1, 6

(3) 2, 1, 2

(4) 3, 1, 4

Correct Answer: (2)

2. An alkali is titrated against an acid with methyl orange as an indicator, find out the right combination from the following table?

Correct Answer: (2)

3. xMnO4–+ yC2O42- +zH+ → xMn2+ + 2yCO2+(z/2)H2O

Calculate the values of x, y and z in the reaction.

(1) 5, 2 and 16

(2) 2, 5 and 8

(3) 2, 5 and 16

(4) 5, 2 and 8

Correct Answer: (3)

4. H2SO3(aq) + Sn4+(aq) + H2O(l) → Sn2+(aq) + HSO4–(aq) + 3H+(aq)

Find out the correct statements from the following options?

(1) H2SO3 is the reducing agent because it undergoes oxidation

(2) H2SO3 is the reducing agent because it undergoes reduction

(3) Sn4+ is the reducing agent because it undergoes oxidation

(4) Sn4+ is the oxidizing agent because it undergoes oxidation

Correct Answer: (1)

5. Find out the correct reactions H2O2 that acts as a reducing agent.

(1) H2O2 + 2H+ + 2e– → 2H2O

(2) H2O2 -2e– → O2+2H+

(3) H2O2 + 2e– → 2OH–

(4) H2O2 + 2OH– -2e– → O2 + 2H2O

(1) (1), (3)

(2) (2), (4)

(3) (1), (2)

(4) (3), (4)

Correct Answer: (2)

6. What number of electrons are there in the following redox reaction?

Cr2O72- + Fe2+ + C2O42- → Cr3+ + Fe3+ + CO2 (Unbalanced)

(1) 3

(2) 4

(3) 5

(4) 6

Correct Answer: (4)

7. Find out the redox reaction from the following options.

(1) XeF4 + O2F2 → XeF6 + O2

(2) XeF2 + PF5 → [XeF]+ PF6–

(3) XeF6 + H2O → XeOF4 + 2HF

(4) XeF6 + 2H2O → XeO2F2 + 4HF

Correct Answer: (1)

8. Find out the redox reaction from the list mentioned below

(1) NaCl + KN03 → NaN03 + KC1

(2) CaC204 + 2HC1 → CaCl2 + H2C20,

(3) Mg(OH)2 + 2NH4C1 → MgCl2 + 2NH4OH

(4) Zn + 2AgCN → 2Ag + Zn(CN)2

Correct Answer: (4)

9. What is the maximum number of electrons transferred in each case in a situation where KMn04 acts as an oxidising agent and ultimately forms [MnO42-, MnO2, Mn2O3 and Mn+2.

(1) 4, 3, 1, 5

(2) 1, 5, 3, 7

(3) 1,3, 4, 5

(4) 3, 5, 7,1

Correct Answer: (3)

For the redox reaction: Zn(s) + Cu2+ (0.1 M)→ Zn+ (1M) + Cu(s) taking place in a cell, E°cell is 1.10 volt. Ecell for the cell will be (2.303 RT / F = 0.0591)

(1) 2.14 V

(2) 1.80 V

(3) 1.07 V

(4) 0.82 V

Correct Answer: (3)

JEE Main Study Notes for Redox Reactions: Preparation Tips

In the section below some important tips for the preparation of JEE Main Redox Reaction are given below.

• Understand not Mug Up

Redox reactions involve a lot of equations. While it may be easy to mug up the requations, try to focus on the principle of the reaction rather than its outcome. Understanding the principle of reactions, would cut down on the equations to remember in the topic.

• Revise Important Reactions on a Periodic Basis

Reactions involving Oxygen, Iron (Fe), Aluminum (Al), Copper (Cu) are most important. Revise and practice them regularly on a weekly basis.

• Remember the Oxidation Numbers

Oxidation numbers play an important part in solving redox equation. So, do remember the oxidation number and states of different elements. The chart of oxidation numbers of common elements is given above.

• Solve Previous Year Questions & Mock tests

It is important for candidates to solve previous year question papers. It helps candidates to be aware of the exam pattern and type of questions that come in JEE Main examination. Solving PYQs will help in time management and candidates will be able to keep a check on their performance.

Time Required for Preparation and Difficulty Level

Redox reactions form the core concept of Electrochemistry, Titration and Electrolysis. Although it can be completed in a week or so, if rushed, it is advised to at least give the topic two weeks in order to fully understand it. The topic is moderately difficult for candidates. Click for help regarding JEE Main Chemistry preparation