Lesson Plan | Traditional Methodology | Reactions: Redox Equation

Objectives

Duration: (10 - 15 minutes)

The purpose of this stage is to provide students with a clear and detailed understanding of the concept of redox reactions. This includes the variation of the oxidation number (nox) of the substances involved and the identification of oxidizing and reducing agents. This understanding is essential for students to follow and absorb the content that will be presented throughout the class, facilitating problem-solving and the practical application of acquired knowledge.

Main Objectives

1. Understand that the redox equation involves the variation of the oxidation number (nox) of substances.

2. Identify the substances that undergo oxidation and reduction in a redox reaction.

3. Differentiate oxidizing agents from reducing agents in a redox equation.

Introduction

Duration: (10 - 15 minutes)

The purpose of this stage is to provide students with a rich and detailed initial context about the theme of the lesson, highlighting the importance and presence of redox reactions in various aspects of life and technology. This will help capture students' interest and contextualize the content that will be covered, facilitating understanding and connection to the real world.

Context

Start the class by explaining that redox reactions are fundamental in many natural and industrial processes. They are present in cellular respiration, photosynthesis, metal corrosion, energy production in batteries, and even in metal purification. Redox reactions involve the transfer of electrons between substances, altering the oxidation number (nox) of the elements involved. This concept is essential for understanding many chemical reactions and everyday phenomena.

Curiosities

Did you know that redox reactions are a crucial part of the functioning of the batteries we use in our cell phones and other electronic devices? Additionally, they play a vital role in gold purification, where oxidation and reduction are used to remove impurities and obtain pure metal. These examples show how redox reactions are important in our daily lives and modern technology.

Development

Duration: (60 - 70 minutes)

The purpose of this stage is to deepen students' understanding of redox reactions by providing them with a solid foundation in the concepts of oxidation and reduction, oxidation number, balancing redox equations, and identifying oxidizing and reducing agents. Through a combination of detailed explanations and practical examples, this section aims to ensure that students are able to effectively apply these concepts to chemical problems and everyday situations.

Covered Topics

1. Definition of Redox Reactions: Explain that oxidation-reduction (redox) reactions involve the transfer of electrons between reactants, resulting in the variation of the oxidation number (nox) of the elements involved. Detail that oxidation is the loss of electrons, while reduction is the gain of electrons. 2. Oxidation Number (Nox): Describe the oxidation number concept as a tool for tracking the transfer of electrons. Provide examples of how to determine the nox of different elements in simple and complex compounds. 3. Balancing Redox Equations: Demonstrate the process of balancing redox equations, first using the oxidation and reduction method and then the ion-electronic method. Provide detailed, step-by-step examples of how to balance redox equations. 4. Identification of Oxidizing and Reducing Agents: Explain that the oxidizing agent is the substance that receives electrons (and thus is reduced) while the reducing agent is the substance that donates electrons (and thus is oxidized). Give clear examples to illustrate the identification of agents in different redox reactions. 5. Applications of Redox Reactions: Discuss some practical applications of redox reactions, such as in industry, biology (cellular respiration and photosynthesis), and in everyday life (batteries).

Classroom Questions

1. Determine the oxidation number (nox) of chromium in the compound Cr2O7^2-. 2. Balance the following redox equation using the ion-electronic method: MnO4^- + Fe^2+ → Mn^2+ + Fe^3+. 3. Identify the oxidizing agent and the reducing agent in the reaction between H2 and O2 to form H2O.

Questions Discussion

Duration: (10 - 15 minutes)

The purpose of this stage is to ensure that students have correctly understood the concepts and procedures presented during the lesson, providing an opportunity to review and consolidate knowledge. Through detailed discussion of the answers and active student engagement, this stage aims to clarify doubts, reinforce learning, and promote the critical application of concepts in different contexts.

Discussion

• Question 1: Determine the oxidation number (nox) of chromium in the compound Cr2O7^2-.

• To determine the nox of chromium in the dichromate ion (Cr2O7^2-), one must remember that oxygen generally has a nox of -2. Since there are seven oxygen atoms, the total nox of the oxygens is -14. The sum of the oxidation numbers of the elements in the ion must equal the charge of the ion, which is -2. Therefore:

• 2 * (nox of Cr) + 7 * (nox of O) = -2

• 2 * (nox of Cr) + 7 * (-2) = -2

• 2 * (nox of Cr) - 14 = -2

• 2 * (nox of Cr) = 12

• nox of Cr = 12 / 2 = +6

• Therefore, the oxidation number of chromium in the Cr2O7^2- ion is +6.

• Question 2: Balance the following redox equation using the ion-electronic method: MnO4^- + Fe^2+ → Mn^2+ + Fe^3+.

• Step 1: Write the oxidation and reduction half-equations:

• Oxidation: Fe^2+ → Fe^3+ + e^-

• Reduction: MnO4^- + 8H^+ + 5e^- → Mn^2+ + 4H2O

• Step 2: Balance the electrons in the half-equations:

• Oxidation: Fe^2+ → Fe^3+ + e^- (multiply by 5)

• 5Fe^2+ → 5Fe^3+ + 5e^-

• Reduction: MnO4^- + 8H^+ + 5e^- → Mn^2+ + 4H2O

• Step 3: Add the half-equations together:

• 5Fe^2+ + MnO4^- + 8H^+ → 5Fe^3+ + Mn^2+ + 4H2O

• The balanced equation is: 5Fe^2+ + MnO4^- + 8H^+ → 5Fe^3+ + Mn^2+ + 4H2O.

• Question 3: Identify the oxidizing agent and the reducing agent in the reaction between H2 and O2 to form H2O.

• In the reaction 2H2 + O2 → 2H2O, hydrogen is oxidized and oxygen is reduced. Therefore:

• Oxidizing agent: O2 (accepts electrons and is reduced)

• Reducing agent: H2 (donates electrons and is oxidized)

Student Engagement

1. What are the essential steps to determine the oxidation number (nox) in a compound? 2. Why is it important to balance redox equations? What could happen if this is not done correctly? 3. How can you quickly identify the oxidizing agent and the reducing agent in a redox reaction? 4. Can you think of more everyday examples where redox reactions occur? Share them with the class. 5. How are redox reactions applied in industry? Provide specific examples.

Conclusion

Duration: (10 - 15 minutes)

The purpose of this stage is to review and consolidate the concepts presented during the lesson, ensuring that students understand the importance and application of redox reactions. This section also aims to connect theoretical content with practical examples, reinforcing the relevance of the study for everyday life and various fields of science and technology.

Summary

• Redox reactions involve the transfer of electrons between reactants, resulting in the variation of the oxidation number (nox) of the elements involved.
• Oxidation is the loss of electrons, while reduction is the gain of electrons.
• Oxidation number (nox) is a tool for tracking the transfer of electrons.
• The oxidizing agent is the substance that receives electrons and is reduced; the reducing agent is the substance that donates electrons and is oxidized.
• Balancing redox equations can be done using the oxidation and reduction method or the ion-electronic method.
• Applications of redox reactions include cellular respiration, photosynthesis, metal corrosion, batteries, and metal purification.

The lesson connected theory to practice by demonstrating how redox reactions are essential in natural and industrial processes, exemplifying everything from cellular respiration to the functioning of batteries and the purification of metals, facilitating students' understanding of the practical application of these concepts in everyday life.

The study of redox reactions is fundamental to understanding many everyday phenomena and industrial processes. For example, metal corrosion can be avoided or controlled by understanding these reactions, and the efficiency of the batteries we use daily also depends on this knowledge. Additionally, vital biological processes, such as cellular respiration and photosynthesis, are based on redox reactions.