CORNERSTONE - Water Quality: Testing Samples

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Objective

SWBAT perform simple water quality tests on a sample, then compare their results to others in the class.

Big Idea

Water quality is measured as a total analysis of varying test results, many of them measured by using chemical reactions.

Why This Lesson?

Today students will apply chemistry to understanding water quality, a real world application of the science.  The water samples tested today are samples that were collected by students who volunteered to collect over the previous weekend, adding to the authenticity of our study.  Students will have already gained a background in what the tests are, what they mean, and how they are performed in the prior day's lesson, Water Quality: How is it Measured?

Evaluating 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 testing 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.

Classroom Video: Tying Lab Investigation to Real World Concepts

Pre-Lab

10 minutes

In the previous day's lesson (Water Quality: How Is It Measured?), students completed a jigsaw activity during which they learned about each different water quality test.  Out of those nine tests, we will only be performing eight, since we have no way to use the Secchi disk in order to gauge turbidity unless we are out in the field at the water source.  Students are familiar with the tests--what they measure, how they relate to water quality, and how each is performed.  Because we spent enough time learning about the tests in a different lesson, today's focus can be on simply performing each test and collecting all of the necessary data.

Not all results will be immediate.  Some tests require days to reach final results (such as the fecal coliform and biochemical oxygen demand tests).  We will continue to check in with these vials over the next few days, looking for possible changes.  Our next several lessons all deal with water quality, so having tests that take longer do not interfere with our studies.  In fact, having tests that take longer actually keep our discussion going and as we learn more, we can discuss more deeply the issues surrounding water quality.

During prelab, I have students unpack their lab baskets (which I had prepared earlier by simply placing the equipment and testing supplies they would need to complete the investigation in large baskets for distribution) by asking them to identify specific items inside.  For example, I will ask students to find the pipette that is sealed in a wrapper.  Some students will not know what to look for exactly, but they all can identify the wrapped item.  I reinforce that they did it correctly when they hold up each item I am calling for.  I also tape each item to the white board and label the board so that if students forget (which they often do) which item is which, they can refer to the board later in the period.

I hand out Water Quality Testing to each student for the recording of their data.

I briefly give instructions for each test, and I can go through them quickly because students have already studied each test's description the day before.  I also encourage students to delegate tasks in order to collect as much data as possible today.

Classroom Video: Student Delegation of Tasks

Lab Investigation

30 minutes

First, students will delegate tasks and divide the workload.  As they are doing this, I am moving around the room to make sure that they are moving forward.  Most groups dive right in, however, occasionally there will be a group who is busy arguing about what to do or a group that is stalled, just waiting for someone to step up and take the lead and nobody does.  In those rare cases (I had it happen with one group in each class period), I can step in and get the group moving quickly by making a suggestion or saying that they have one minute to get on track or I will assign tasks.  This usually gets things moving in a productive direction.

Once tasks are delegated, students quickly move into task mode and work on their individual tests.  I engage students in thinking about what they are doing by asking questions (why are you doing it that way?) or asking them to explain to me what they are doing.  I ask questions not because students are wrong, but because I want to build their confidence in being able to justify their actions.

During investigation time, I also reinforce the use of proper academic vocabulary terms: Classroom Video: Building Academic Vocabulary

As time winds down, I remind students to keep working and to finish up before class is over.

Consolidating Results & Analyzing Data

15 minutes

As groups begin to finish collecting testing data, it is important for all of the students in a group to know the testing results of their sample.  Students begin to share their individual results with the rest of their group and, in order to fill in the rest of the table on their handout, they must know what the test results mean and what it says about their sample.

During this discussion time among the small group, I am moving through the room looking for students to be engaged in respectful discussion (Classroom Video: Respectful Discussions) and for them to be able to reach consensus (Classroom Video: Teaching Students to Reach Consensus) when possible.

As I check in with groups, I may ask some follow up questions that students do not immediately know the answers for.  In these instances, it is important that I wait long enough to give students the opportunity to successfully answer my questions, as described here: Classroom Video: Wait Time.

Tomorrow, we begin by looking at the data from today's lesson and discussing the possible implications.

Note: We found that the LA River water samples had high levels of fecal coliform bacteria, and low levels of nitrates and phosphates.  Students determined that to mean that possibly that water is being contaminated with sewage (causing the bacteria growth), but that overall, the water quality is allowing for a thriving plant and bird habitat.  We found that Venice Beach water samples had low levels of fecal coliform bacteria, which was unexpected because there is coastal sewage outflow.  Students were happy to find that Venice water quality was actual pretty good.  Students were also happy to find that our tap water was high quality, further reason not to purchase bottled water.

Samples of Student Data Tables:

I appreciate this student's honesty about being confused (in the "Overall Thoughts" section).  This tells me that it is really important to go back and discuss our results, spending time debriefing to make sure that students learn from the data analysis.

Sections left blank in the data table are blank because those tests are either ones we are not performing (i.e. turbidity) or ones that take longer than one period to get the results.