Objectives (5 - 7 minutes)

1. Understand the concept of common concentration: Students should be able to understand what the common concentration of a solution is, comprehending its formula and how it is calculated. They should also be able to identify situations where the use of common concentration is appropriate.

2. Solve problems involving common concentration: Students need to be able to apply the acquired knowledge to solve practical problems involving common concentration. They should be able to determine the mass of solute needed to prepare a solution of a given concentration, or determine the concentration of a given solution given the mass of the solute and the volume of the solvent.

3. Recognize the importance of common concentration in everyday life: Students should be able to identify examples of the use of common concentration in everyday situations, such as in food and beverage preparation, or in the dilution of medications.

   Secondary Objectives:

   • Develop problem-solving skills: In addition to learning the concepts related to common concentration, students should also be able to apply these concepts to solve problems. This includes the application of formulas, the use of correct units, and the interpretation of results.

   • Promote critical thinking: By solving problems involving common concentration, students will be encouraged to think critically about the application of the concepts learned and to reach logical conclusions. This will help develop their critical thinking skills, which are valuable in many areas of life beyond chemistry.

Introduction (10 - 15 minutes)

1. Review of previous content: The teacher should start the lesson by reviewing the concepts of solution, solute, and solvent, as well as the difference between a diluted and concentrated solution. This can be done through interactive questions to assess the students' level of understanding and to ensure that everyone is on the same page before moving on to the new content.

2. Problem situation: The teacher can then present two problem situations involving common concentration. For example, he can ask students how much salt they would need to add to a glass of water to make a brine solution with a concentration of 10%. Or, he can ask students how much sugar they would need to add to a glass of water to make a sugar solution with a concentration of 20%. These questions serve to introduce the topic and to show students the relevance of common concentration in the real world.

3. Contextualization: The teacher should then contextualize the topic, explaining how common concentration is used in everyday life. He can discuss how cooks use common concentration to make syrups, sauces, and marinades, and how doctors use common concentration to dose medications. This will help motivate students by showing the practical applicability of what they are about to learn.

4. Capturing students' attention: To make the Introduction more engaging, the teacher can share some curiosities or stories related to the topic. For example, he can mention that the original Coca-Cola was sold as a medicine and that its formula included a concentration of 9% phosphoric acid. Or, he can tell the story of how the Swedish chemist Svante Arrhenius developed the theory of ionic dissociation while studying the concentration of electrolytes in solution. These stories serve to capture students' attention and make the topic more memorable.

Development (20 - 25 minutes)

1. Role-Playing Activity: Chemical Kitchen (10 - 12 minutes)

   • Scenario: The teacher divides the class into groups of 4 to 5 students. Each group will receive a recipe for a dessert that must be prepared in the classroom. However, the recipe does not indicate the exact amount of ingredients to be used, only the required concentration of each ingredient in the final solution.

   • Task: Students must use the formula for common concentration to determine the correct amount of each ingredient to be used. They should consider the mass of the solute (ingredient) and the volume of the solvent (another part of the recipe that is not the solute) to calculate the concentration.

   • Resources: The teacher should provide students with a table containing the density and concentration of each ingredient that will be used in the activity. Students can also use calculators to facilitate calculations.

   • Outcome: At the end of the activity, each group should have a list of the quantities of ingredients needed to prepare the dessert. The teacher can then discuss the answers with the class and verify if the calculations were done correctly.

2. Practical Activity: Preparing Solutions (10 - 12 minutes)

   • Scenario: The teacher provides groups of students with several bottles of mother solution (highly concentrated solution), distilled water, and a series of empty containers (cups, beakers, etc.). Each mother solution has a different concentration, and students must prepare solutions with specific concentrations.

   • Task: Students must use the formula for common concentration to determine the amount of mother solution and the amount of distilled water needed to prepare the desired solution. They should consider the total volume of the solution (mother solution + distilled water) and the desired concentration.

   • Resources: Students can use calculators to facilitate calculations. The teacher should be available to answer any questions and provide guidance as needed.

   • Outcome: At the end of the activity, each group should have prepared several solutions with different concentrations. The teacher can then check the concentration of each solution using a refractometer or other appropriate instrument.

3. Results Discussion (5 - 8 minutes)

   • After the conclusion of the activities, the teacher should lead a classroom discussion to review the concepts learned and to clarify any doubts students may have. He can ask students to explain how they solved the problems and to share any challenges they faced. The teacher can then provide feedback and additional guidance, if necessary, to ensure that all students understood the material.

   • The teacher can also use this time to reinforce the importance of common concentration in everyday life, discussing additional examples and answering students' questions. This will help consolidate students' knowledge and show the relevance of the topic.

Return (8 - 10 minutes)

1. Group Discussion (3 - 4 minutes): The teacher should gather all students and start a group discussion. He can ask representatives from each group to share the solutions they found for the Role-Playing and Preparing Solutions activities. This is an opportunity for students to learn from each other, checking different approaches to solving the same problems. The teacher should ensure that all students have the chance to speak and that all viewpoints are respected.

2. Connection to Theory (2 - 3 minutes): Next, the teacher should make the connection between the practical activities and the theory of common concentration. He should highlight how the calculations students performed in the activities reflect the concept of common concentration and how this concept is applied in practice. The teacher can use examples from the activities to illustrate the points he is making and can ask students to provide their own examples.

3. Individual Reflection (2 - 3 minutes): Finally, the teacher should propose that students reflect individually on what they learned in the lesson. He can ask questions like:

   • What was the most important concept you learned today?
   • What questions have not been answered yet?
   • How can you apply what you learned today in your everyday life?

   The teacher should give students a minute to think about these questions and then can ask some volunteers to share their answers. This will give the teacher an idea of what students understood and which areas may need further review or clarification in future classes. Additionally, this activity helps promote metacognition in students, which is the ability to reflect on their own learning.

4. Feedback and Closure (1 - 2 minutes): At the end of the lesson, the teacher should thank the students for their participation and effort. He can also give brief feedback on students' performance, highlighting strengths and areas that may need more practice. The teacher should encourage students to continue studying the subject at home and to ask questions if they have difficulties. He can also provide additional resources, such as practice exercises, explanatory videos, or links to relevant websites.

Conclusion (5 - 7 minutes)

1. Summarization (2 - 3 minutes): The teacher should recap the main points covered during the lesson. This may include the definition of common concentration, the formula for calculating common concentration, and the application of common concentration in everyday situations. He should ensure that all key concepts were understood by the students and answer any remaining questions.

2. Connection between Theory and Practice (1 - 2 minutes): The teacher should emphasize how the lesson connected the theory of common concentration with practice. He can mention how the Role-Playing and Preparing Solutions activities allowed students to apply theoretical concepts in a practical and meaningful way. This will help reinforce the importance of active learning and motivate students to apply what they have learned.

3. Extra Materials (1 minute): The teacher should suggest additional materials for students who wish to deepen their understanding of the topic. This may include books, articles, websites, videos, or chemistry apps that offer clear explanations and practice exercises. The teacher can also provide a list of practice exercises for students to complete at home in order to consolidate what they learned in the lesson.

4. Importance of the Topic (1 minute): Finally, the teacher should emphasize the importance of common concentration in everyday life. He can mention again examples of how common concentration is used in different contexts, such as in food preparation, chemical manufacturing, and medicine. This will help show students that chemistry is not just an abstract academic discipline, but something that has practical and relevant applications in their daily lives.