Context

Stoichiometry is the calculation of the relative quantity of reactants and products in a chemical reaction. It is one of the most fundamental concepts in chemistry, as it is present not only in school but in many practical aspects of everyday life and in various industrial areas.

In stoichiometry, we deal with the molecular proportions in which substances react with each other. When we have chemical reactions, we do not always have the substances in ideal quantities; some end up running out, remaining in excess, while others are completely consumed, thus being the limiting reagent. Discovering which substances are in excess or are limiting in a chemical reaction is essential to calculate the efficiency and profitability of a chemical process.

Stoichiometry, specifically the concepts of limiting reagent and excess reagent, has immense practical applications. The chemical industry needs to carefully control the quantities of reagents to maximize efficiency and minimize waste. In cooking, the proportions of ingredients are important for the success of a recipe.

Therefore, understanding this topic will not only help you stand out in your future career in chemistry but also in your everyday life. To delve deeper into this topic, I recommend the following resources:

1. Khan Academy: Stoichiometry (https://www.khanacademy.org/science/chemistry/chemical-reactions-stoichiome) - A series of detailed videos and practical exercises to help you understand and master stoichiometry.
2. Brasil Escola: Stoichiometry (https://en.brasilescola.uol.com.br/chemistry/stoichiometry.htm) - A complete and easy-to-understand introduction to stoichiometry.
3. Chemistry Manual: Ponderal Laws and Stoichiometry (https://www.chemistrymanual.com/general-chemistry/stoichiometry.htm) - In-depth articles on the fundamentals and applications of stoichiometry.

Practical Activity: "Stoichiometric Duel: Limiting vs Excess"

Project Objective

The proposed activity aims to reinforce the concept of stoichiometry and provide students with a practical understanding of the topics of "limiting reagent" and "excess reagent." Additionally, the activity encourages teamwork, problem-solving, creativity, and time management.

Project Description

Students will be divided into groups of 3 to 5 people, and each group will receive a kit of trivial and safe chemical reactions that can be carried out in the school environment. Each kit will have all the necessary reagents, but the quantities of the reagents vary, forcing students to identify which ones are in excess and which is the limiting reagent.

The group must carry out the chemical reaction, record the entire process, calculate the quantities of reagents and products, identify the limiting reagent and the excess reagent, and then prepare a detailed report on the experiment.

Required Materials

• Chemical reaction kit (the necessary quantity will be provided by the school)
• Scale
• Stopwatch
• Temperature measurement device
• Personal protective equipment (goggles, gloves, and apron)
• Camera for recording the experiment
• Notebook for notes
• Computer with Internet access

Step by Step

1. Each group will receive the chemical reaction kit and a detailed description of the reaction, including the balanced chemical equation.

2. The group must weigh all the reagents using the scale to identify which reagent is in excess and which is the limiting reagent.

3. Perform the experiment using the stopwatch and the temperature measurement device to record the reaction time and temperature variation.

4. Record all observations during the experiment, including changes in states, coloration, gas emissions, among others.

5. Calculate the amount of products formed in the reaction.

6. Identify which reagent(s) remained at the end of the reaction.

7. Prepare a detailed report of the experiment, including the description of the reaction, the amount of reagents used, the identification of the limiting reagent and the excess reagent, the calculation of the amount of products formed, the analysis of the data obtained in the experiment, and the conclusion on the importance of stoichiometry in chemical reactions.

Project Delivery

At the end of the project, each group must deliver:

• Complete experiment report in Word or PDF format containing:

1. Introduction: Should contain the contextualization of the theme, its relevance and application in the real world, and the objective of this project.
2. Development: Should describe the theory of stoichiometry, the detailed description of the experiment performed, the methodology used, the discussion of the results obtained, and the identification of the limiting reagent and the excess reagent.
3. Conclusion: Should contain a summary of the main points of the work, the learnings obtained, the conclusions drawn about the project, and the importance of stoichiometry concepts in everyday chemical processes.
4. Bibliography: Should indicate the sources they relied on to work on the project such as books, web pages, videos, etc.

• Documentary video of the experiment performed, including the execution of the reaction, the observations, the identification of the limiting reagent and the excess reagent, and a brief discussion on the results.

The project delivery must be made within a week from the start date of the activity.