Today students will apply chemistry to improving water quality. They will be using nanoparticles to remove common contaminants like metallic ions and larger organic molecules (mimicking typical water contaminants we see in real life). This engages students in materials science--they will see that the two different types of cleaning particles we use interact with the contaminant molecules/ions in different ways, leading to an understanding of both HS-PS1-3 (Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.) and HS-PS2-6 (Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.).
Students will have already gained a background in how water quality is measured and will have participated in testing real samples from the community in the two prior lessons: Water Quality: How is it Measured? and Water Quality: Testing Samples.
Treating water samples and exploring sources of poor quality water will help students meet Performance Expectation HS-ESS3-6: Use a computational representation to illustrate the relationships among Earth systems and how those relationships are being modified due to human activity. Students will be cleaning samples, engaging in SEP 3: Planning and Carrying Out Investigations. They will also be analyzing those results, participating in SEP 4: Analyzing and Interpreting Data. As students finish collecting data, they will be challenged to explain why zeolite and carbon work to clean the particles that they do, explaining what interactions are occurring on a molecular level, addressing SEP 6: Constructing Explanations.
This investigation is lengthy--there are many steps to follow and students have difficulty navigating the procedure at times. In order to allow enough time for completion AND to allow students time to digest the procedure (and diagram it so that they understand what they will be doing), I stretch this activity over two days. The first day lesson can be found here: Water Quality: Removing Contaminants Day 1.
This procedure is provided by UCLA's California NanoScience Institute. The procedure, background information, and other resources can be found here: CNSI High School Program Water Purification. Note: Teachers in the UCLA area can attend free workshops to carry out the lab and get free student materials!!
Instead of doing a Warm-Up today, it is important to jump right in to finishing up our lab procedure. I do, however, want to check in with the working groups as a whole class and give the opportunity for questions. My goal is to see if there are any common stumbling blocks thus far and to help make sure everyone feels ready to go and on track for completing the activity today.
Students work in their groups to finish the lab procedure for the rest of the period. As groups do finish, I advise them to clean all of their equipment and their tables. I handout the Discussion Questions from UCLA (available here) and a copy of the Background information included on their website (available here) to help them be able to answer the Discussion Questions.
Student #1 demonstrates a general understanding that the cleaning particles work on certain contaminants, but she does not clarify the difference in function between the activated carbon and the zeolite. (She also doesn't show her work for calculating molar masses--a pretty big no-no in my class.) Student #2 demonstrates a much deeper understanding of why the filters alone do not remove the contaminants (the contaminants are smaller than the filter pore size). She also explains why zeolite does not remove the yellow food coloring but activated carbon does (the zeolite is attracted to positive charges and the food coloring is uncharged, however, the activated carbon is attracted to the large organic molecule). Student #3 is an English Learner, however, he is still ableto demonstrate understanding that zeolite and carbon act differently, but he does not explain that difference. I can ask him directly to better gauge through conversation what he did understand and what he did not.
Once students have finished their investigation and have cleaned up, I want to discuss our results. I ask what students found as they completed the investigation. Some results:
I ask if anyone has heard of 'Lifestraw' and how it works. Many do not recognize the proper name, but when I describe Lifestraw as a filtering tool that is often used in developing countries with no clean running water, several of my students then recognize the product. Then I show my students this video to reinforce what we just did in lab and how there is a real world application of this work: