Contextualization

The concepts of pH and pOH are fundamental in Chemistry, especially in Analytical and Environmental Chemistry. The pH indicates the acidity, basicity, or neutrality of a solution, being crucial for the determination of chemical compounds, and the pOH is the expression for the molar concentration of hydroxide ions (OH-) in a solution.

The pH scale ranges from 0 to 14, where 7 indicates a neutral solution, values below 7 indicate acidic solutions, and above 7, basic solutions. On the other hand, pOH is calculated using the same scale but to determine the basicity of a solution. The sum of pH and pOH always results in 14, at a temperature of 25°C.

In Chemistry, changes in pH can affect the structure and activity of molecules, and therefore, understanding these concepts is important in various applications of Chemistry.

In the food industry, for example, pH is important to control the growth of microorganisms in preserved foods. In the human body, the blood pH needs to be maintained around 7.4 to ensure the proper functioning of various biological functions. In environmental terms, pH can affect aquatic life, which typically prefers a pH range between 6.5 and 9.

Understanding these concepts and applying them correctly can have a significant impact in various areas of science. Therefore, the objective of this project is to deepen your knowledge about pH and pOH and discover how these concepts are applied in practice.

For introduction and deepening into the topic, the following resources can be used:

• Book "Chemistry: The Central Science", by Brown, LeMay, and Bursten.
• Article "The importance of studying pH and neutralization processes in Chemistry education"
• YouTube channel Química em Ação, by Professor Paulo Valim, with classes and illustrative experiments.

Practical Activity: "Discovering the Acid-Base World: An Immersion in pH and pOH"

Project Objective:

To develop, in groups of 3 to 5 students, a simple experiment to observe the changes in pH and pOH in acidic, basic, and neutral solutions, using common and easily replicable measurement methods. In the end, write a complete report about the experience.

Activity Description:

The project will consist of conducting experiments using two household substances (such as lemon juice, baking soda, water, etc.) and a pH indicator (litmus paper or red cabbage indicator), measuring the pH and pOH values, and discussing the implications of these values in a real context.

Required Materials:

1. Two household substances (lemon juice, baking soda, water, vinegar, etc.)
2. Litmus paper or red cabbage indicator
3. Distilled water (can be boiled for sterilization)
4. Two colorless glass cups
5. A pH meter (can be found in stores selling products for pools or chemical laboratories)
6. Pencil and paper for notes

Step by Step:

1. Form groups of 3 to 5 students. Each group should choose two substances to test.

2. Make a test solution by mixing the chosen substance with distilled water in a glass cup.

3. Dip a piece of litmus paper or a bit of red cabbage indicator into the solution and observe the color change.

4. Note the observed color and consult the color scale of the litmus paper or red cabbage indicator to determine the pH value.

5. Calculate the pOH of the solution by subtracting the pH value from 14.

6. Repeat steps 2 to 5 for the second substance.

7. Discuss the observations and interpretations as a group, considering what was learned in the classes about pH and pOH, and make a prediction about the behavior of other substances.

After the practice, each group should produce a report containing:

• Introduction: Description of what pH and pOH are, their importance and application in real situations, in addition to the purpose of the experiment conducted.

• Development: Detailed description of the methodology used, presentation and discussion of the results obtained, along with a theoretical explanation justifying the results.

• Conclusion: Summary of what was learned, linking theory and the results of the experiment, and pointing out possible practical applications of what was learned.

• Bibliography: Citation of all information sources used for the project development.

Project Deliverables:

The final result of this project will be a report written by each group, including all the aspects mentioned above (Introduction, Development, Conclusions, and Bibliography). Additionally, students must be able to demonstrate an understanding of the concepts of pH and pOH and their practical application.