Water Quality: Removing Contaminants Day 1

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Objective

SWBAT describe potential contaminants (such as large organic molecules and metallic ions), where they come from, and how to remove them from water samples.

Big Idea

Water pollutants from industry are usually in the form of large organic molecules and metallic ions; we can remove these contaminants using small particles to "soak" up the contaminants.

Why This Lesson?

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.  

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 second day lesson can be found here: Water Quality: Removing Contaminants Day 2.  

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!!

Warm-Up

5 minutes

While I take attendance, students do a warm-up activity in their composition Warm-Up/Reflection books.  I use warm-ups to either probe for students' prior knowledge about the day's upcoming lesson or to have them bring to mind and review what they should have learned previously.  (To read more about Warm Up and Reflection Books please see the attached resource.)

Today’s Warm-Up: “What are some ways to improve water quality?”

In this case, the warm-up is asking students to draw upon their prior knowledge to think about practical uses of chemistry as it applies to improving water quality.  It is also preparing students for today's activity during which they will be learning about cleaning particles and how to use them to remove particular contaminants.  Tomorrow's lesson will involve actual cleaning of water samples to determine which cleaning particles are appropriate for removing which contaminants.

If time permits, I walk around with a self-inking stamp to stamp the completed warm-ups indicating participation, but not necessarily accuracy.  In order to speed things up, my students have been trained to pass their books into the center of the table rows and stack them so that I can quickly pass by and stamp.  On days when there is too much business keeping, I do not stamp.  Students have been told that warm-ups are occasionally immediately checked and other times not.  At the end of each unit, Warm-Up/Reflection Books are collected and spot-checked.  Today, I do stamp books.  We do not discuss answers to the pre-lab question because students will discover the answer during today's activity.  Many students answer that one way to improve water quality is to filter it, which is interesting because tomorrow students will mimic carbon filtering.

Pre-Lab Discussion

10 minutes

Before handing out the lab procedure, I explain that students will be removing contaminants from water samples.  I ask students what kinds of things can contaminate water and expect to get a range of answers.  In particular, I will steer the conversation towards runoff of pesticides and the contamination of metallic ions (which they are familiar with from the movie "Erin Brokovich," part of our curriculum for their Environmental Technology class which they take concurrently with this Chemistry class).

Then I explain that we can use "cleaning particles" to trap the contaminants, and when we filter the cleaning particles out afterwards, we remove the contaminants along with those particles.  I tell my students that we will be using zeolite and carbon as our two cleaning particles and their job is to determine which particle works on which type of contaminant.  This is all leading to an assessment where they will need to clean contaminated water samples later: ASSESSMENT: Removing Contaminants and Balancing pH of a Water Sample.

I pass out the lab procedure from UCLA's California NanoScience Institute.  I cannot share the handouts here, but they can be requested from this webpage.  I did find an instructional video posted on YouTube that is very quick, but can be paused to see all of the procedural steps and the materials used.

 

Pre-Lab Activity

20 minutes

The lab procedure itself is very dense, with 31 different steps.  This can be overwhelming for anyone, let alone a high school student.  In order to scaffold this procedure and to make sure that everyone knows what each step entails, I give students a graphic organizer to diagram their steps.  I handout Water Filtration Experiment - Diagramming the Procedure and instruct students to draw and use abbreviated notes to fill in the table with each step.  I allow students about 20 minutes to go through this process.  

Student samples:

Front only

Front and Back

Front and Back

Front only

I was impressed by students' ability to pick apart the procedure and translate it into something that made sense for them.  Most students used a combination of drawing and words, but samples here are pretty representative of the range of student work.

Student Investigation, Day 1

20 minutes

As students finish diagramming their procedures, they are ready to start grouping up in order to start their investigation.  I have enough materials that students can store their solutions in the provided vials without impeding the next class period's access to those materials.  

I handout a sheet provided by UCLA that organizes samples as the groups work.  The sheet has labeled areas for each vial and students label the vials #1-#8 with masking tape in order to make sure they do not get mixed up.

Clean-Up

5 minutes

As we get close to the end of the period, I give students a five minute warning and advise them to begin cleaning up.  I remind students to label their vial organizing sheet with group names and to put all of their supplies in their group's lab basket.  The names on the vial sheet will help students identify their basket during Day 2 of this activity.  Groups store their lab baskets on a lab station in the back of the classroom.