Context

Stoichiometry is an essential tool in chemistry that allows predicting the quantities of products and reactants involved in a chemical reaction. This discipline deals with the quantitative relationship between elements in a reaction, enabling scientists to predict the amounts of necessary reactants and the products that will be formed.

Since ancient times, alchemists sought to better understand the relationship between the quantities of reactants and products, and it was from the 19th century onwards that the concept of stoichiometry began to be more clearly defined. Today, this tool is invaluable for chemists, pharmacists, chemical engineers, and biologists seeking to understand and manipulate chemical reactions.

However, the application of stoichiometry goes beyond laboratories and classrooms. It is extremely useful in various areas, from the industrial production of materials, medicines, and food to waste treatment and predicting the effects of global warming. Therefore, no matter what career you choose, stoichiometry will likely be useful for you!

Stoichiometry is the basis for understanding many important chemical processes, including determining limiting and excess reagents.

In every chemical reaction, there is a precise amount of reactants that react to form products. However, in practice, there may be an excess reagent, meaning it is present in a larger quantity than necessary to completely react with the other reagent. Meanwhile, the other reagent, known as the limiting reagent, is present in insufficient quantity and will be completely consumed, thus determining the amount of product formed.

These concepts are fundamental in chemistry and have significant practical applications. For example, in chemical industries, production costs can be minimized by adjusting the proportion of reagents so that the more expensive reagent becomes the limiting one. Additionally, many chemical reactions do not occur as expected due to limiting reagents, and understanding this concept allows scientists to optimize their reactions.

Practical Activity

Activity Title: Stoichiometry Lab: Limiting Reagent and Excess Reagent

Project Objective:

The objective of this project is to understand the concepts of stoichiometry, limiting reagent, and excess reagent. Through a practical experiment, students should be able to calculate the quantities of reactants and products involved in a reaction, identify which reagent is limiting and which is in excess, and understand how these concepts apply in real life.

Detailed Project Description:

This project will be carried out in groups of 3 to 5 students and will last for one month. The group will conduct a practical experiment, in which they will have to identify the limiting reagent and the excess reagent. The experiment will involve the production of oxygen gas from the decomposition of hydrogen peroxide in the presence of a catalyst.

The groups should then write a detailed laboratory report, including the introduction, development, conclusions, and bibliography used. This report should describe the theory behind the concepts of stoichiometry, limiting reagent, and excess reagent, the steps of the experiment, the results obtained, and the conclusions drawn from these results.

In practical terms, the groups must be able to perform stoichiometric calculations to predict the quantities of product that will be formed in the reaction and identify the limiting reagent and the excess reagent.

Required Materials:

• Hydrogen peroxide (H2O2)
• Catalyst: potassium iodide solution or yeast.
• Scale
• Erlenmeyer flask
• Graduated cylinder
• Dropper
• Stopwatch
• PPE: Safety goggles, gloves, and lab coat.

Activity Steps:

1. Prepare the hydrogen peroxide solution, measuring the required amount with the graduated cylinder.
2. Place the hydrogen peroxide solution in the Erlenmeyer flask.
3. Add the catalyst to the Erlenmeyer flask.
4. Observe the reaction and record your observations.
5. Perform stoichiometric calculations to determine the limiting reagent and the excess reagent.
6. Write a laboratory report detailing the experiment results. The introduction section should explain the concepts of stoichiometry, limiting reagent, and excess reagent. The development section should explain the experiment in detail, including the methodology used and the results obtained. The conclusions section should include a discussion on predictions versus results obtained and the understanding of the concepts learned. Finally, the bibliography section should list all sources used for the experiment and report preparation.

Connection Between Suggested Activities and Project Deliverables:

Students will be conducting a practical experiment where they will apply the theoretical knowledge learned about stoichiometry, limiting reagent, and excess reagent. The connection between the activity and the final project deliverable is the student's ability to apply theory in practice and reflect on the results obtained through the report writing. The report will allow students the opportunity to consolidate their learning by explaining in detail the concepts learned, the methodology used in the experiment, and reflecting on the results obtained.