Contextualization

Chemistry study allows us to understand how substances interact with each other, transform themselves, and how their structure influences this behavior. One of these aspects is solubility, which describes how much of a substance (solute) can be dissolved in another (solvent). In this project, we will delve into the understanding of a very important concept related to solubility: the Solubility Product, or Kps, which allows us to predict whether or not a precipitation reaction will occur.

Kps is defined as the product of the molar concentrations of the ions in a saturated solution, each raised to its stoichiometric coefficient in the salt dissociation equation. This means that Kps is a constant that describes the equilibrium between the salt solid and its ions in solution when the solution is saturated. If the solution is not saturated, the dissolution reaction can still proceed until saturation is reached. However, if the solution is saturated and the temperature remains constant, the relationship between the concentrations of the ions is constant and is given by the Kps.

Thus, the study of Kps is extremely important in Chemistry and in everyday life. It allows, for example, industries and laboratories to predict whether or not a salt will dissolve in a solution, which can be crucial in the preparation of a chemical reaction. In our body, Kps helps us to understand the processes of dissolution and precipitation of inorganic salts, such as those that occur in the formation of kidney stones. In addition, Kps is also fundamental to the understanding of water and effluent treatment processes, as it allows us to predict the precipitation of salts that may be harmful to the environment or human health.

To deepen your understanding on this subject, we recommend using the following resources:

1. Book "General Chemistry and Chemical Reactions", by John Kotz, Paul Treichel and John Townsend. Cengage Learning Publisher.
2. Video lesson "Solubility Product - Kps" on the Chemistry in Action channel with Prof. Paulo Valim, available on YouTube.
3. Website "Brasil Escola", specifically the Chemistry section, where you can find several texts on the topic of solubility and Kps.
4. Website "Mundo Educação", also in the Chemistry section, with focus on solutions and chemical equilibrium.

Practical Activity

Activity Title: "Know the Kps: From Theory to Practice"

Project objective:

The activity aims to provide students with a deeper understanding of the concept of solubility product (Kps) and to show its applications. Students will calculate the Kps of an inorganic salt in the laboratory, carry out experiments to verify the veracity of the calculated value, and analyze the effect of the common ion on solubility.

The activity will involve the disciplines of Chemistry and Mathematics, and students will have to apply concepts of chemical equations, solution concentrations, statistics and data analysis.

Detailed description:

Students will be divided into groups of 3 to 5 people and each group will have to:

1. Choose a soluble inorganic salt for which they will determine the Kps. This choice should be justified in the final report.

2. Calculate the theoretical Kps of the chosen salt from information available in textbooks and/or scientific articles.

3. Experimentally determine the Kps of the chosen salt. To do this, students will have to prepare a saturated solution of the salt, measure its concentration, and then calculate the Kps.

4. Carry out experiments to verify if the prepared solution is really saturated, and if the experimentally calculated Kps value is correct.

5. Carry out experiments to observe the effect of the common ion on the solubility of the chosen salt, and explain the results based on theory.

Required materials:

• Soluble inorganic salt
• Analytical scale
• Beaker
• Glass rod
• Distilled water
• Oven
• Spectrophotometer
• Solution standards for spectrophotometer calibration

Step by step:

1. Weigh a known quantity of the chosen salt and dissolve it in a known volume of distilled water to prepare a saturated solution.
2. Take the solution to the oven until all the salt is dissolved.
3. Measure the absorbance of the solution in the spectrophotometer.
4. Compare the absorbance with a known solution standard to determine the salt concentration in the solution.
5. Calculate the Kps from the salt concentration in the solution.
6. Repeat the experiment several times to obtain an average value for the Kps.
7. Record all data and calculations in the laboratory notebook.
8. Write the final report, including a discussion of the effect of the common ion on the solubility of the chosen salt.

Project deliverables:

Students must submit a detailed report of their experience and the results obtained. The report should follow the following structure:

1. Introduction: Contextualization of the topic, its relevance and application in the real world, and the project objective.
2. Development: Theory behind the main theme of the project, detailed description of the activity, methodology used, presentation and discussion of the results obtained.
3. Conclusion: Summary of the main points, lessons learned and conclusions drawn from the project.
4. Bibliography: Indication of the sources used to work on the project.

Students should demonstrate, through the report and through the work developed, that they have acquired the technical and socio-emotional skills mentioned above.