Contextualization

In the field of Chemistry, the concentration of a solution is a measure of how much of a given solute is dissolved in a certain volume of solvent. Common concentration, specifically, is a way to express this concentration in terms of the solute's mass and the solution's volume. Knowing how to calculate common concentration is a fundamental aspect to understand how chemical reactions occur in solutions.

Throughout our lives, we constantly come across solutions of different concentrations. The water we drink, the soft drinks we consume, the medicines we take, all are solutions. Therefore, understanding what common concentration is and how to calculate it is extremely important, not only to study chemical reactions, but also to better understand the world around us.

Introduction

Common concentration (C) is a measure of the ratio of solute mass (m) to solution volume (V). It is calculated by the formula C = m/V. Usually, mass is expressed in grams and volume in liters, so the unit of common concentration is g/L, grams per liter.

But why is it important to calculate common concentration? Imagine you are a pharmacist and need to prepare a solution of a medicine for a patient. You need to ensure that the amount of active ingredient in the solution is correct, so that the medication is effective without being harmful. For this, it is necessary to calculate the solution's concentration.

Finally, common concentration is not the only way to measure solution concentrations. There are others like molality and molarity, each suitable for different situations. Understanding which one to use in each situation is an important part of studying Chemistry.

Practical Activity – Preparation and analysis of solutions

Project Objective

The objective of this activity is to apply the concepts of common concentration in the preparation and analysis of different solutions of table salt (NaCl) in water. Students will calculate the common concentration of the solutions and correlate it with their density.

Detailed Project Description

Groups of 3 to 5 students will be responsible for preparing four different NaCl solutions in water, with predefined concentrations, and calculate the density of these solutions. Additionally, they should write a detailed report of the experiment, including the introduction, development, conclusions, and bibliography used.

Required Materials

• Precision balance
• 100 mL beakers
• Table salt (NaCl)
• Distilled water
• 100 mL graduated cylinder
• 25 mL graduated pipette
• Rubber bulb for pipetting
• Hydrometer

Step-by-Step for Activity Execution

1. Prepare the four NaCl solutions in water with the following concentrations: 5 g/L, 10 g/L, 15 g/L, and 20 g/L. To do this, use the formula C = m/v to calculate the necessary salt mass. For example, to prepare 100 mL of a 10 g/L solution, dissolve 1 g of NaCl in water to complete 100 mL.
2. Weigh the solutions using the precision balance and record.
3. Measure the volume of the solutions with the graduated cylinder and record.
4. Use the hydrometer to measure the density of the solutions and record.
5. Tabulate the results obtained and create a graph of concentration versus density.
6. Write the report following the guidelines below.

Project Deliverables

Students must submit a written report containing:

Introduction

In this section, students should describe the experiment's objective, the importance of common concentration in Chemistry, and everyday situations where these concepts are applied.

Development

Here, students should detail the process of preparing the solutions, with a detailed description of the steps taken and the results observed. This is the moment to demonstrate understanding of the theory behind the concepts involved, using the formulas and calculations performed to prepare the solutions.

Conclusions

Students should analyze the results obtained, discuss the relationship between concentration and the solutions' density, and how understanding this concept is relevant to Chemistry. They should also mention any difficulties encountered during the experiment and how they were overcome.

Bibliography

Students should list all sources of information used for the project, including books, websites, and videos.

This project should be carried out over a period of 2 to 3 weeks, considering the time for preparing the solutions, conducting measurements, analyzing the results, and writing the report.