Concentration and Solubility Mark as Favorite (4 Favorites)
In this activity, students will use news articles and EPA publications to compare Federal drinking water regulations to the concentrations found in Flint, Michigan. Students are introduced to the unit parts per billion (ppb) and compare it both conceptually and mathematically to molarity. As a group, students use data to compare the solubility of various lead salts and perform solubility calculations.
This activity will help prepare your students to meet the performance expectations in the following standards:
- HS-ETS1-3: Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.
- Scientific and Engineering Practices:
- Using Mathematics and Computational Thinking
- Developing and Using Models
- Analyzing and Interpreting Data
By the end of this activity, students should be able to:
- Define the unit parts per billion (ppb).
- Differentiate between ppb and molarity.
- Analyze and interpret data from a box and whisker plot.
- Understand solubility data.
- Accurately complete concentration calculations.
This activity supports students’ understanding of:
Teacher Preparation: 5 - 10 minutes
Lesson: 90 minutes
- Student Handout
- Periodic Table
- Internet Access
- No specific safety precautions need to be observed for this activity.
- To learn more about this activity, read the associated article, Exploring Social Justice Through a Chemistry Lens, featured in the May 2023 issue of Chemistry Solutions.
- This activity is intended to be used as the second part of a semester-long project. Unlike a typical project that is confined to a particular unit or topic, the Flint Water Crisis is used as a focal point of the larger project and is revisited as needed throughout the semester. A variety of chemistry topics and activities are connected to it during this time.
- Teachers can use this particular activity independent of the larger project or review the related article for more information about the activities that precede and follow this one. In the five-part project, students apply concepts including solution chemistry, stoichiometry, and electrochemistry to the ongoing water crisis in Flint, Michigan. In the process, they also learn about both the science and the societal impact of this issue.
- In this activity students will analyze a Box and Whisker Plot as part of their investigation.
- It may be helpful to review these types of graphs with the entire class.
- Boxes and lines are used to visualize the distribution of data. The “box” contains 50% of the data, with a line indicating the median point of the data. The lines that extend are the “whiskers” which indicate the remaining range of data. Any dots shown are outliers.
- Additional background information about Box and Whisker plots can be found through references below:
- An Answer Key document is included for teacher reference.
For the Student
Conduct background research related to drinking water and the Flint Water Crisis in order to answer the following questions. Cite any sources used. Much of the information can be found in the Washington Post Article, “This is how toxic Flint’s water really is”.
- Lead concentration in drinking water is usually measured in “parts per billion” (ppb).
- What does this unit of concentration mean?
- When measuring water contamination, parts per billion is often expressed at “micrograms per liter” (μg/L). Explain in words or use math to show that 1 ppb is equivalent to 1 μg/L. (Hint: consider that the density of water = 1g/mL)
- According to the Environmental Protection Agency (EPA), what is the maximum concentration of lead allowed in safe drinking water in ppb?
- What lead concentrations have been found in the Flint, MI water supply in ppb? This will be dependent on the location, so find one or two values and cite your sources.
- Initially, some Flint residents began boiling their water in hopes that this would make it safe to drink. This led to billboards like the one shown warning the public. What would boiling their water do to the lead concentration? Include boiling point information for lead and water to support your claim.
|Figure 1. © Carl Ganter/Circle of Blue. Use with permission.|
Figure 2. Water lead levels in August 2015 collected through a citizen science sampling campaign based on service line material. Action level (15 μg/L) denoted by gray line. Water lead levels <1 μg/L were set to 0.5 μg/L. FD= first draw; 1MF= 1 min flush sample (water was allowed to flow for 1 minute before taking sample) ; 3MF = 3 min flush sample (water was allowed to flow for 3 minutes before taking sample).
Source: Kelsey J. Pieper, Rebekah Martin, Min Tang, LeeAnne Walters, Jeffrey Parks, Siddhartha Roy, Christina Devine, and Marc A. Edwards. Environmental Science & Technology 2018 52 (15), 8124-8132
- The graph shown in Figure 2 is a “Box and Whisker Plot” from a study of Flint, Michigan water published in the journal “Environmental Science & Technology”.
- What values are represented on the y-axis of the graph?
- What unit of concentration is used to measure lead levels?
- What is the meaning of “FD”, “1MF” and “3MF” on the x-axis mean? (Hint: read the figure 2 caption.)
- What is the median first flush (FD) lead level for each type of pipe?
- What do you notice about lead concentrations for “first flush” samples as compared to “1 min flush” and “3 min flush” samples? What does this data suggest to you?
- According to the graph, what types of pipes produce the highest lead concentrations?
- What additional questions or ideas do you have after studying the data displayed on the graph?
Solubility (g/100 mL at 20oC)
- Lead occurs in a variety of different ionic compounds. The solubilities of some of these compounds are listed in the table above. Use this information to answer the following questions:
- What is the maximum number of grams of lead (II) oxide that could dissolve in 25.0 mL of water at 20oC?
- Calculate the molarity (M) of a saturated solution of lead (II) oxide. Show your work.
- A saturated solution of which lead salt would have the lowest concentration? Explain.
- Draw a particle diagram showing the water molecules and the ions present when lead (II) carbonate dissolves. Be sure to consider the orientation of the water molecules.