Objectives (5 minutes)

1. Understand the concept of dilution: The teacher should guide the students to understand what dilution of a solution is, explaining that it consists of reducing the solute concentration in a solution by adding more solvent. It should be emphasized that dilution does not involve removing the solute from the solution, but rather decreasing its concentration by adding more solvent.

2. Calculate the final concentration of a diluted solution: The teacher should instruct the students on how to calculate the final concentration of a solution after dilution. This involves understanding the formula C1V1 = C2V2, where C1 is the initial concentration, V1 is the initial volume, C2 is the final concentration, and V2 is the final volume.

3. Apply the concept of dilution in practical situations: The teacher should encourage students to apply the concept of dilution in everyday practical situations and chemistry problems. This will help reinforce the understanding of the concept and the ability to calculate the final concentration of a diluted solution.

Secondary objectives:

• Stimulate critical thinking: The teacher should encourage students to think critically about how dilution affects the concentration of a solution. This can be done through questions and discussions during the class.

• Promote teamwork: The teacher can organize group activities to encourage collaboration among students and the development of teamwork skills.

Introduction (10 - 15 minutes)

1. Review of previous contents: The teacher should start the class by briefly reviewing the concepts of solution, solute, solvent, and solution concentration. This is essential for students to understand the new content of dilution. It may be helpful to ask students questions or have them explain these concepts to ensure they have a good prior understanding.

2. Problem situation 1: The teacher can present a scenario in which a student needs to prepare a diluted solution for an experiment. However, the student is unsure how to calculate the amount of solute and solvent needed to achieve the desired concentration. This will serve to arouse students' interest in the importance of dilution calculation and how this knowledge can be useful.

3. Contextualization: The teacher should highlight the importance of dilution and its use in various areas, such as in the pharmaceutical industry for the preparation of medications, in the production of food and beverages, and even in everyday life, when diluting juices or soft drinks, for example.

4. Problem situation 2: The teacher can present another scenario in which a scientist needs to prepare a solution with a specific concentration for an experiment, but only has a more concentrated solution and water available. Students should be challenged to think about how the scientist could dilute the solution to achieve the desired concentration.

5. Capturing students' attention: To draw students' attention to the topic, the teacher can share some curiosities, such as the fact that dilution is used in the production of medicines to ensure the correct dose is administered to patients, or that dilution can be used to 'mask' the taste of stronger alcoholic beverages, making them smoother.

6. Introduction of the topic: Finally, the teacher should introduce the topic of the class, dilution of solutions, explaining that they will learn how to calculate the final concentration of a diluted solution, as well as understand the processes and practical applications of dilution.

Development (20 - 25 minutes)

1. Theory presentation (10 - 15 minutes):

   1.1. Definition of dilution: The teacher should start by explaining what dilution of a solution is, reminding that it consists of reducing the solute concentration in a solution by adding more solvent.

   1.2. Situations involving dilution: Next, the teacher should present some practical situations involving the dilution of solutions, such as the preparation of medications, the production of food and beverages, and even the dilution of juices and soft drinks at home.

   1.3. Dilution formula: The teacher should then introduce the dilution formula, C1V1 = C2V2, explaining that it relates the initial concentration (C1) and initial volume (V1) of the solution to the final concentration (C2) and final volume (V2) of the solution after dilution.

   1.4. Examples of dilution: To illustrate the concept, the teacher should present some examples of dilution, showing step by step how to apply the dilution formula. Examples may include the dilution of medications, the dilution of juices and soft drinks, and the dilution of solutions in the laboratory.

   1.5. Calculation of the final concentration: The teacher should then explain how to calculate the final concentration of a solution after dilution. This involves understanding that the amount of solute in the solution does not change during dilution, only its concentration.

2. Practical activities (10 - 15 minutes):

   2.1. Problem solving: The teacher should propose some dilution problems for students to solve in groups. The problems should vary in difficulty, allowing students to practice applying the dilution formula in different contexts. The teacher should move around the classroom, guiding the groups and clarifying doubts.

   2.2. Experimental activity: The teacher can carry out an experimental activity to demonstrate the dilution of a solution in practice. For this, a container with a concentrated solution (which can be, for example, concentrated juice), a bucket of water (the solvent), and disposable cups will be needed. The teacher should pour the concentrated solution into one of the cups and then gradually add water while students observe the change in the color and taste of the solution. The teacher should explain that the addition of water is diluting the solution, decreasing the solute concentration.

   2.3. Group discussion: After solving the problems and conducting the experimental activity, the teacher should lead a group discussion on the importance of dilution and its applications in different contexts. This will help students consolidate what they have learned and understand how dilution is used in practice.

Return (10 - 15 minutes)

1. Connection with theory (5 - 7 minutes): 1.1. Group discussion: The teacher should organize a group discussion on how the practical activities carried out connect with the presented theory. Students should be encouraged to express their opinions and share their conclusions with the class. The teacher should guide the discussion, highlighting the main points and clarifying any misunderstandings. 1.2. Review of the dilution formula: The teacher should review the dilution formula, explaining again how it works and why it is useful for calculating the final concentration of a diluted solution. Students should be encouraged to ask questions and clarify any doubts they may still have.

2. Individual reflection (3 - 5 minutes): 2.1. Reflective questions: The teacher should propose some questions for students to reflect on individually. The questions may include: 1. How would you describe the dilution process in your own words? 2. What was the most important concept you learned today? 3. What questions do you still have about dilution? 2.2. Time for reflection: The teacher should give students a few minutes to reflect on these questions. This will allow them to consolidate what they have learned and identify any areas they still do not fully understand.

3. Student feedback (2 - 3 minutes): 3.1. Student comments: The teacher should invite students to share their answers to the reflective questions, as well as any other comments or observations they may have about the class. 3.2. Appreciation and encouragement: The teacher should thank the students for their participation and encourage them to continue striving to understand the material. Any questions or difficulties that still exist should be noted to be addressed in future classes.

4. Closure (1 minute): 4.1. Summary of the class: The teacher should summarize the main points covered in the class, reinforcing the concept of dilution, the dilution formula, and the practical applications of dilution. 4.2. Preparation for the next class: The teacher should inform students about what will be covered in the next class, and if there are any homework assignments or readings that need to be done to prepare them for the new content. 4.3. Farewell: Finally, the teacher should bid farewell to the students, reminding them to study and review the class material to ensure they have a good understanding of the topic.

Conclusion (5 - 7 minutes)

1. Summary of the class (2 - 3 minutes): The teacher should recap the main points covered during the class, recalling the definition of dilution, the dilution formula (C1V1 = C2V2), and the practical applications of dilution. It should also highlight the importance of understanding and correctly applying the dilution formula to calculate the final concentration of a diluted solution. Additionally, the teacher should recall the performance of the practical activity and the group problem-solving of dilution.

2. Theory-practice connection (1 - 2 minutes): The teacher should emphasize how the class managed to connect theory and practice, explaining that the theoretical presentation was followed by practical activities that allowed students to apply what they learned. It should also mention the group discussion, which allowed students to share their conclusions and exchange ideas about dilution.

3. Extra materials (1 minute): The teacher should suggest some extra materials to complement students' understanding of dilution. This may include explanatory videos, chemistry websites with examples and solved exercises, and chemistry textbooks. For example, the teacher may recommend a video demonstrating the dilution of a solution in practice, or a website offering dilution problems for students to solve at home.

4. Relevance of the topic (1 minute): Finally, the teacher should emphasize the importance of the class topic for students' daily lives. It should explain that dilution is a very common operation in various areas, such as in the pharmaceutical industry, in the production of food and beverages, and even in everyday life, when diluting juices or soft drinks. It should also mention that the ability to calculate the final concentration of a diluted solution is very useful in various professions and fields of study, and may be required in exams and tests.