Objectives (5 - 7 minutes)

1. Understand the concept of chemical equations and the importance of balancing them.
2. Learn to identify redox reactions and apply the oxidation number method to balance the equations.
3. Develop skills to balance chemical equations, including redox equations, through practice of problems and exercises.

Secondary Objectives:

• Familiarize with different types of chemical reactions and their characteristics.
• Learn to calculate the oxidation number of an element in a substance.
• Develop the ability to apply the oxidation number method to balance chemical equations.

Introduction (10 - 15 minutes)

1. The teacher should start the class by briefly reviewing the basic concepts of chemical reactions, including what reactants and products are, and how they are represented in a chemical equation. The teacher should emphasize that, although a chemical equation may seem correct at first glance, it actually needs to be balanced to be correct. (3 - 5 minutes)

2. Next, the teacher should introduce the concept of redox reactions, explaining that they are reactions in which electron transfer occurs between chemical species. The teacher can give examples of redox reactions in everyday life, such as iron rusting (oxidation) and the reduction of oxygen in cellular respiration. (3 - 5 minutes)

3. The teacher should then introduce the concept of oxidation number, explaining that it is a number that indicates the oxidation state of an atom in a substance. The teacher can give examples of how to calculate the oxidation number in different compounds, such as water (H2O) and carbon dioxide (CO2). (2 - 3 minutes)

4. To spark students' interest, the teacher can share some curiosities or applications related to the topics of the class. For example, they could mention that balancing chemical equations is crucial in many industrial processes, such as the production of medicines and food. Another curiosity could be that the concept of oxidation-reduction is fundamental to understanding biological phenomena, such as respiration and photosynthesis. (2 - 3 minutes)

5. The teacher should then present the objective of the class, which is to learn how to balance redox equations using the oxidation number method. Additionally, it should be highlighted that the class will involve a combination of theory and practice, with students having the opportunity to solve problems and equations during the class. (1 - 2 minutes)

Development (20 - 25 minutes)

1. Theory Presentation (10 - 12 minutes)

   1.1. The teacher should start the theory by explaining that to balance a chemical equation, it is necessary for the total number of atoms of each element to be the same in the reactants and products. The teacher can illustrate this with a simple example, such as the formation equation of water from hydrogen and oxygen (2H2 + O2 -> 2H2O).

   1.2. Next, the teacher should introduce the concept of redox equations, explaining that they are equations in which a redox reaction occurs. The teacher can illustrate this with the same example of water formation, explaining that hydrogen is oxidized (loses electrons) and oxygen is reduced (gains electrons).

   1.3. The teacher should then present the oxidation number method to balance redox equations. The teacher should explain that the oxidation number is a number that indicates whether an atom has gained or lost electrons and that, in a redox reaction, the oxidation number of some atoms changes.

   1.4. The teacher should explain that to balance a redox equation using the oxidation number method, it is necessary to follow the following steps:

    1.4.1. Identify the species that are oxidized and reduced in the reaction.
    
    1.4.2. Write the oxidation and reduction half-reactions, which show the transfer of electrons.
    
    1.4.3. Balance the oxidation and reduction half-reactions, first by equalizing the number of oxygen atoms, then the number of hydrogen atoms, and finally the number of electrons.
    
    1.4.4. Sum the balanced half-reactions, canceling the electrons that appear on both sides of the equation.
    
    1.4.5. Check if the equation is balanced.
    
   

   1.5. The teacher should then explain that the oxidation number method is a powerful tool for balancing redox equations, but it can be a bit complex at first. Therefore, it is important to practice a lot to gain skill.

2. Example Resolution (10 - 13 minutes)

   2.1. The teacher should then solve some examples of balancing redox equations using the oxidation number method. The examples should start with simple equations and become more complex as students gain confidence.

   2.2. While solving the examples, the teacher should explain each step of the process, highlighting key points and common difficulties.

   2.3. The teacher should encourage students to ask questions and participate actively in the class, promoting discussion and critical thinking.

   2.4. The teacher should then assign some problems for students to solve individually or in groups. The problems should be varied and challenging, yet still achievable. The teacher should move around the room, helping students who are struggling and providing feedback on their work.

3. Practical Activity (5 - 7 minutes)

   3.1. To consolidate learning, the teacher should propose a practical activity. This activity can be a simple experiment, a computational simulation, or a real-world problem involving redox equations.

   3.2. During the activity, the teacher should encourage students to apply what they have learned and think critically about solving the problem.

   3.3. After the activity conclusion, the teacher should lead a classroom discussion, allowing students to share their solutions and discuss the difficulties they faced. The teacher should take this opportunity to reinforce the key concepts and skills of the class.

Return (8 - 10 minutes)

1. Group Discussion (3 - 4 minutes)

   1.1. The teacher should start the Return phase by asking students to share the solutions or conclusions they found during the practical activity. Each group should have a maximum of 2 minutes to present.

   1.2. During the presentations, the teacher should encourage students to explain the reasoning behind their solutions and make connections with the theory discussed in class.

   1.3. The teacher should facilitate the discussion by asking questions to clarify points of confusion, encouraging the participation of all students, and ensuring that discussions are respectful and constructive.

2. Connection with Theory (2 - 3 minutes)

   2.1. After the presentations, the teacher should give a brief review of the main concepts and procedures discussed during the class. The teacher should emphasize how the theory applies to the practice of balancing redox equations.

   2.2. The teacher should then connect the concepts learned with the skills needed to solve redox equation problems. For example, the teacher can explain how the ability to identify the species that are oxidized and reduced in the reaction is crucial for balancing redox equations.

   2.3. The teacher should also reinforce the importance of the oxidation number method, explaining how it simplifies the process of balancing redox equations.

3. Individual Reflection (2 - 3 minutes)

   3.1. To end the class, the teacher should propose that students reflect individually on what they have learned. The teacher should ask questions like:

    3.1.1. What was the most important concept you learned today?
    
    3.1.2. What questions have not been answered yet?
    
    3.1.3. How can you apply what you learned today in other situations?
   

   3.2. The teacher should give students a minute to think about these questions and then open the discussion for students to share their reflections, if they wish. The teacher should listen carefully to the students' answers and make notes for future reference.

   3.3. To conclude the class, the teacher should reinforce the importance of continuous practice to improve the skills of balancing redox equations and encourage students to continue studying the topic outside the classroom.

Conclusion (5 - 7 minutes)

1. Summary of Contents (2 - 3 minutes)

   1.1. The teacher should start the Conclusion by recapping the main points covered in the class. The definition of redox equations, the concept of oxidation number, and the method for balancing redox equations should be reviewed.

   1.2. The teacher should emphasize that to balance a chemical equation, it is necessary for the total number of atoms of each element to be the same in the reactants and products. Additionally, it should be remembered that in a redox reaction, the oxidation number of some atoms changes.

   1.3. The teacher should summarize the steps of the oxidation number method for balancing redox equations and reinforce that practice is essential to gain skill in this process.

2. Connections between Theory and Practice (1 - 2 minutes)

   2.1. The teacher should then explain how the class connected the theory of balancing redox equations with practice. It should be emphasized that the oxidation number method, which was discussed theoretically, was applied in practice to solve redox equation problems.

   2.2. The teacher should reinforce that by making this connection, students were able to see the relevance and applicability of the theoretical concepts.

3. Supplementary Materials (1 - 2 minutes)

   3.1. The teacher should then suggest supplementary study materials for students. These materials may include chemistry books, educational websites, explanatory videos, and online practice exercises.

   3.2. The teacher should emphasize that reviewing these materials outside the classroom can help students consolidate what they have learned and prepare for future classes or assessments.

4. Topic Importance (1 minute)

   4.1. To conclude the class, the teacher should highlight the importance of balancing redox equations in everyday life and in various areas of science and industry.

   4.2. The teacher can mention examples of how understanding redox equations is crucial in various contexts, such as in energy production in batteries, water purification, medicine synthesis, among others.

   4.3. Additionally, the teacher should emphasize that developing skills in balancing redox equations can help students improve their problem-solving skills, logical reasoning, and critical thinking, which are valuable skills in many aspects of life.