Lesson plan of Concentration Units: Molarity

Objectives (5 - 7 minutes)

1. Understanding the concept of Molarity: The teacher needs to ensure that students understand what molarity is and how it is calculated. This includes explaining the concept of a mole and its relationship to molarity. Students should be able to define molarity in their own words and apply this definition to practical problems.

2. Molarity Calculations: Students should be able to perform molarity calculations, using the correct formula and appropriate units of measurement. This involves converting between different units of measurement and applying the concept of molarity to real-world situations.

3. Application of Molarity: The teacher should ensure that students understand how molarity is used in practice, especially in chemical reactions. This may include examples of how molarity affects the rate of a reaction, the amount of product formed, and the amount of reactant required.

Secondary Objectives:

• Developing Problem-Solving Skills: Through molarity calculations, students should be able to develop their problem-solving skills, including the ability to think logically and analytically.

• Promoting Active Participation: The teacher should encourage active participation from students throughout the lesson, asking questions, soliciting examples, and encouraging discussion. This will help ensure that students are engaged and understanding the material.

Introduction (10 - 15 minutes)

1. Review of Prior Knowledge: Before introducing the new content, the teacher should briefly review the concepts of the mole and concentration, which are fundamental to understanding molarity. This review can be done by asking students direct questions, encouraging them to recall what they have already learned. (3 - 5 minutes)

2. Problem Situation: To pique students' interest and show the applicability of the concept that will be studied, the teacher can propose two problem situations:

   • Imagine that you need to prepare a 0.5 mol/L solution of table salt (NaCl). How would you make this preparation? (The goal here is to get students thinking about how to use molarity to calculate the amount of solute needed to prepare a solution of a given concentration.)

   • Suppose you have a 2 mol/L solution of hydrochloric acid (HCl) and need to dilute it to obtain a 0.2 mol/L solution. How much water should you add? (In this situation, the idea is for students to apply the concept of molarity to calculate the amount of initial solution and the amount of water needed to obtain the desired solution.) (5 - 7 minutes)

3. Contextualization: The teacher should explain that molarity is a fundamental concept in chemistry, widely used in research laboratories and chemical industries. Additionally, it can be mentioned that the calculation of molarity is frequently used in university entrance exams and chemistry olympiads. (2 - 3 minutes)

4. Curiosities and Applications: To pique students' interest, the teacher can share some curiosities and applications related to molarity:

   • Curiosity 1: Molarity is so-called because it is expressed in moles/liter. The term "molar" comes from the Latin "molaris", which means "related to a mole".

   • Curiosity 2: Molarity is used not only to express the concentration of solutions but also to calculate the amount of reagents needed in a chemical reaction.

   • Application 1: Molarity is used in the pharmaceutical industry to calculate the amount of a drug that must be dissolved in a given volume of solvent to obtain a certain concentration.

   • Application 2: Molarity is used in research laboratories to prepare solutions of reagents with precise concentrations, which is crucial for obtaining reliable results in chemical experiments. (3 - 5 minutes)

Development (20 - 25 minutes)

1. Solution preparation experiment: (10 - 12 minutes)

   • Preparation of a table salt solution: The teacher should bring a known amount of table salt (NaCl) to the classroom and instruct students to prepare a 0.5 mol/L NaCl solution.

     • Step 1: The teacher should explain that to prepare the solution, it is first necessary to calculate the amount of NaCl that should be dissolved in a given volume of water. The formula to be used is: n = C x V, where n is the number of moles of NaCl, C is the desired molarity (0.5 mol/L), and V is the volume of the solution in liters.

     • Step 2: After the calculation, students should weigh the necessary amount of NaCl and add it to a volumetric flask.

     • Step 3: Next, students should add water to the volumetric flask until the indicated volume is reached.

     • Step 4: Finally, students should shake the solution to ensure that the NaCl is completely dissolved.

   • Preparation of a diluted hydrochloric acid solution: Next, the teacher should instruct students to prepare a 0.2 mol/L hydrochloric acid (HCl) solution from a concentrated 2 mol/L HCl solution.

     • Step 1: The teacher should explain that preparing a diluted solution involves adding solvent to the initial solution. The formula to be used is: C1V1 = C2V2, where C1 is the molarity of the initial solution, V1 is the volume of the initial solution, C2 is the molarity of the diluted solution, and V2 is the volume of the diluted solution.

     • Step 2: Students should calculate the volume of initial solution that should be used, as well as the volume of water that should be added.

     • Step 3: After the calculation, students should measure the amount of initial solution and water using pipettes and add them to a volumetric flask.

     • Step 4: Finally, students should shake the solution to ensure thorough mixing.

   The teacher should circulate around the room, assisting students and clarifying any doubts. At the end of the experiment, the solutions prepared by the students should be tested with pH strips to check if the molarity was calculated correctly.

2. Discussion of the experiment: (5 - 7 minutes)

   • The teacher should propose a discussion about the steps of the experiment, the calculations performed, and the results obtained.

   • Students should be encouraged to express their opinions and share their experiences during the experiment.

   • The teacher should ask questions to verify whether students understood the concept of molarity and how it was applied in the experiment.

3. Application activity: (5 - 6 minutes)

   • After the discussion, the teacher should propose an application activity in which students must calculate the molarity of a solution from the data of a chemical reaction.

   • The teacher should provide the reaction data (balanced chemical equation and amount of reactants and products) and students should calculate the molarity of the formed solution.

   • The teacher should circulate around the room, assisting students and clarifying any doubts. At the end of the activity, students should share their answers and the teacher should correct them if necessary.

4. Reinforcement activity: (2 - 3 minutes)

   • To reinforce the learning, the teacher should propose a final activity in which students must solve molarity problems.

   • The teacher should provide a list of problems, each with a different level of difficulty, and students should try to solve them.

   • The teacher should circulate around the room, assisting students and clarifying any doubts. At the end of the activity, the teacher should correct the problems and clarify any remaining doubts.

Feedback (8 - 10 minutes)

1. Group discussion: (3 - 4 minutes)

   • The teacher should gather the students and promote a group discussion about the solutions found by each one for the molarity problems proposed in the reinforcement activity.
   • The teacher should encourage students to explain how they arrived at their answers, share the strategies they used, and discuss the difficulties they faced.
   • The teacher should clarify any misconceptions or misunderstandings that may arise during the discussion and ensure that all students have correctly understood the concept of molarity.

2. Connection to theory: (2 - 3 minutes)

   • The teacher should then make the connection between practice (experiment and activities) and theory (concept of molarity and calculations).
   • The teacher should explain how the practice helped reinforce the understanding of the theory, and how the theory, in turn, could be applied to solving practical problems.
   • The teacher should emphasize the importance of understanding the theory to be able to apply it correctly in practical situations, and vice versa.

3. Individual reflection: (2 - 3 minutes)

   • The teacher should propose that students reflect individually on what they learned during the lesson.
   • For this, the teacher can ask questions such as:
     1. What was the most important concept you learned today?
     2. What questions have not yet been answered?
   • Students should be encouraged to write down their answers in a notebook or on a piece of paper.
   • The teacher should clarify that the answers do not need to be shared with the class, but that the teacher will be available to answer any questions students may have.

4. Teacher feedback: (1 - 2 minutes)

   • Finally, the teacher should give general feedback on the students' participation, understanding of the content, and execution of the activities.
   • The teacher should encourage students to continue practicing molarity calculations at home and to bring any questions to the next class.

Conclusion (5 - 7 minutes)

1. Recapitulation of Key Concepts: (2 - 3 minutes)

   • The teacher should summarize the main points covered during the lesson, reinforcing the concept of molarity and the formula for its calculation.
   • The importance of molarity in chemistry should be highlighted, especially in chemical reactions and in the preparation of solutions.
   • The teacher should briefly review the steps for preparing solutions and diluting solutions, emphasizing the need for accurate molarity calculations in these situations.

2. Connection between Theory, Practice, and Applications: (1 - 2 minutes)

   • The teacher should reinforce how the lesson connected the theory, practice, and applications of molarity.
   • Students should be reminded that the theory was applied in practice through the preparation of solutions and the calculations of molarity, and that these skills have important practical applications in industry and scientific research.

3. Supplementary Materials: (1 - 2 minutes)

   • The teacher should suggest additional study materials for students who wish to deepen their understanding of molarity.
   • These materials may include textbooks, chemistry websites, educational videos, and additional molarity exercises.
   • The teacher should encourage students to explore these materials on their own time and to bring any questions that may arise to the next class.

4. Importance of the Subject: (1 minute)

   • To conclude, the teacher should summarize the importance of molarity for students' everyday lives.
   • It can be mentioned that molarity is used to calculate the amount of ingredients needed to prepare a recipe (for example, when making bread or cooking pasta), and that it is also an important concept for understanding many biological and environmental processes.
   • The teacher should reinforce that mastering molarity is essential for success in future chemistry studies and in many scientific and technical careers.