Contextualization

Chemical concentration is a fundamental concept in chemistry that describes the amount of a particular solute in a solution. In other words, it is a way to express the quantity of a substance in a specific volume of solution. There are several concentration units, such as molarity, molality, normality, mass and volume percent, molar fraction, molar percentage, mass and volume percentage, and parts per million (ppm), just to name a few.

To understand these concentration units, we need to comprehend what solutions are. A solution is a homogeneous mixture of two or more substances. The component present in larger quantity is called the solvent, and the others are called solutes. Solutions are very common in our daily lives. For example, bleach is a solution of sodium hypochlorite in water. Seawater is a solution of salts in water.

Concentration units are important because they determine how a solution will behave in certain chemical reactions. For instance, molarity, which is the amount of moles of solute in one liter of solution, is commonly used in calculations involving chemical reactions in solution. On the other hand, parts per million (ppm) is frequently used in environmental analyses to express the concentration of contaminants in water or air.

Understanding concentration units is essential for the development of analytical skills and the comprehension of the chemical processes that occur around us. In everyday life, various problems require an understanding of these units, such as determining the molarity of acetic acid in the vinegar we have at home or the chlorine concentration in pool water.

Recommended study resources:

1. Khan Academy: Concentration Units
2. Mundo Educação: Common Concentration
3. Brasil Escola: Concentration in Chemistry
4. YouTube: Prof. Igor Alves
5. YouTube: Chemistry in Action - Prof. Paulo Valim

Practical Activity

Activity Title: Solutions Around the World: An Investigation on Concentrations

Project Objective

The objective of this project is to investigate the concentration of solutes in different solutions from our daily lives and the environment. The aim is to demonstrate how important it is to understand and interpret concentration units in their various forms and applications.

Detailed Project Description

For this project, groups of 3 to 5 students will investigate, calculate, and analyze the concentration of two types of solutions:

• A common solution in our daily lives (e.g., salt in seawater, acetic acid in vinegar, sugar in juice, etc.);
• A solution related to an environmental issue (e.g., concentration of heavy metals in river water, pollutants in the air, pesticides in food, etc.).

The groups will need to search for reliable sources to find the necessary data for calculating the concentrations and demonstrate the application of concentration concepts in the chosen solutions.

Once the choices are made, students should calculate the concentrations using the units of molarity, molality, and ppm. Additionally, it is essential for students to investigate the significance and implications of their findings.

Required Materials

• Internet access for research;
• Notebook or digital system for notes and report preparation;
• Calculator.

Step-by-Step for Activity Execution

1. Form groups of 3 to 5 students.
2. Choose the two solutions to be investigated.
3. Research and obtain reliable data for your solutions.
4. Calculate the concentration of the solutions in molarity, molality, and ppm.
5. Investigate and discuss the relevance of your findings in daily life and/or the environment.
6. Write a detailed report of your findings and conclusions.

The estimated duration of the project is 5 to 10 hours per student, and the deadline for submission is one month.

Project Deliverables

The final project submission will be a written report divided into four parts: Introduction, Development, Conclusions, and Bibliography.

Introduction: In this part, students must explain the concept of solution and the concentration units studied. Additionally, they should mention the two chosen solutions for investigation and explain why they made those choices.

Development: Students should present the data found in their research and explain how they calculated the concentrations of their solutions in different units. Here, it is important for students to demonstrate a clear understanding of concentration units and how they apply to the real world.

Conclusions: In this section, students should discuss the meaning of their findings. What do the concentrations found imply? What does this mean for our daily lives or the environment? This is the place to connect theory to practice and demonstrate a deep understanding of the subject.

Bibliography: Indication of the consulted sources. It is important for students to indicate the sources they relied on to work on the project, citing any books, internet pages, videos, among others, that were used.