Background

Concentration is a fundamental concept in chemistry, used to describe the amount of a substance present in a given volume of solution. There are many different units of concentration, such as molarity, molality, normality, and percent by mass. Here, we will focus on a lesser-known but very relevant unit: parts per million (ppm).

Parts per million is often used in contexts where the amounts of a substance are present in very small quantities. For example, we might use ppm to describe the amount of carbon dioxide (CO2) in the atmosphere, or the amount of lead (Pb) in a water sample.

Understanding and being able to calculate concentration units, especially parts per million, is vital in many areas, from monitoring air quality to controlling toxic chemicals in our drinking water. Therefore, it is a highly relevant practical skill, both for everyday life and for future careers in science or engineering.

Hands-on Activity

Activity Title: Concentration Detectives - The Hunt for Parts Per Million

Project Goal:

To gain a practical understanding of the concept of parts per million (ppm) and develop the ability to calculate this unit of concentration. Additionally, to develop soft skills such as teamwork, time management, and problem-solving.

Detailed Project Description:

Groups will be challenged to find the concentration of an "unknown substance" in water, expressed in parts per million (ppm). To do this, they will need to develop a methodology to dilute this substance and calculate its concentration.

Required Materials:

• Unknown substance (e.g., food coloring)
• Water
• Pipettes or other measuring devices
• Analytical balance
• Containers for diluted mixtures
• Calculator

Step-by-Step Activity Procedure:

1. Step 1: Group formation: Students will be divided into groups of 3-5 members.

2. Step 2: Background reading: Each group should read about the concept of parts per million (ppm) and how to calculate this unit of concentration.

3. Step 3: Receiving the unknown substance: Each group will receive a fixed amount of the unknown substance.

4. Step 4: Solution preparation: Each group should add water to the unknown substance until they have a solution. The amount of water added should be recorded.

5. Step 5: Weighing: Each group should weigh the amount of unknown substance in their solution. This will serve as the initial mass of the substance.

6. Step 6: Dilution: Groups should perform serial dilutions of the original solution, recording the volume of solution and the volume of water added at each step.

7. Step 7: Calculating the concentration in ppm: Each group should calculate the concentration of the unknown substance in ppm at each dilution step.

8. Step 8: Report writing: Groups should write a report detailing the entire process and the results obtained.

The activity should take no more than four hours to complete. The total project submission time is one week, including the final report.

Project Deliverables:

Groups are required to submit:

1. Final Report: A written document reporting on the procedures performed and their results. The report should be divided into four main sections:

   • Introduction: The group should provide context on the topic of "parts per million", its relevance and real-world applications, and state the project's objective.

   • Development: The group should explain the theory behind the concept of parts per million, describe the activity in detail, state the methodology used, and present the results obtained, including the measurements and calculations performed.

   • Conclusions: The group should conclude the work by summarizing their main points, stating what they learned from the project, and what conclusions were drawn about the concept of parts per million.

   • Bibliography: The group should list the sources they relied on to complete the project, such as books, web pages, videos, etc.

2. Presentation: Each group will give an oral presentation showcasing the results they obtained and explaining the process they used. They may use graphs, tables, or other visuals to demonstrate their findings.