Water Quality Testing
Objective
Big Idea
Introduction
In this lesson students are planning and performing a lab to understand how to test water quality and to compare tap water versus rain water.
- This lesson does not align with any specific performance expectations with the Next Generation Science Standards; however, I feel that it ties the unit together in regards to solutions, acids and bases.
- This lesson aligns with the Next Generation Science and Engineering Practice 3: Planning and Carrying out Investigations. It does so because students are performing a lab activity where they are performing 7 different tests in regards to water quality.
- This lesson aligns with the Next Generation Science and Engineering Practice 4: Analyzing Data. It does so because students are using their data to come up with differences between tap water and rainwater.
- This lesson also aligns with the Next Generation Science and Engineering Practice 6:Constructing Explanations and Designing Solutions. It does so because students have to write a paragraph explaining how rain water and tap water are similar and different.
For the lab activity I have 7 stations with various materials. At the first 3 stations I use vernier probes. See my reflection on use of probes for more information about the benefits of probeware in your classroom. If you do not have access to probes you could chose to use a pH meter or pH paper for station #3 and skip the first two stations (have students only do 5 stations).:
- At station #1 I have a dissolved oxygen probe, tap water in a labeled 200mL beaker, rain water in a labeled 200mL beaker, and distilled water in a labeled 200mL beaker.
- At station #2 I have a turbidity sensor probe, vial to fit inside the sensor, distilled water in a labeled bottle, rain water in a labeled bottle, and tap water in a labeled bottle.
- At station #3 I have a pH probe, tap water in a labeled 200mL beaker, rain water in a labeled 200mL beaker, and distilled water in a labeled 200mL beaker.
- At station #4 I have a well plate, a dropper bottle of distilled water, a dropper bottle of tapwater, a dropper bottle of rain water, a dropper bottle of 0.1M calcium chloride, and a dropper bottle of 0.1M sodium carbonate.
- At station #5 I have a well plate, a dropper bottle of distilled water, a dropper bottle of tapwater, a dropper bottle of rain water, a dropper bottle of 0.1M iron (III) chloride, and a dropper bottle of 0.1M potassium thiocyanate.
- At station #6 I have a well plate, a dropper bottle of distilled water, a dropper bottle of tapwater, a dropper bottle of rain water, a dropper bottle of 0.1M copper II chloride, and a dropper bottle of 0.1M silver nitrate.
- At station #7 I have a well plate, a dropper bottle of distilled water, a dropper bottle of tapwater, a dropper bottle of rain water, a dropper bottle of 0.1M sodium sulfate, and a dropper bottle of 0.1M barium chloride.
Engage
To begin this lesson I have students read the article "Quest for a clean drink". This article is from the ChemMatters magazine which is published from the American Chemical Society and is available online.
I have students read this article so that they can understand why it is important to be able to test water as well as how engineers have come up with some ways to clean water.
To do this I first pass out the article to students along with a questions paper.
I then have students skim the questions paper so that they will know what to look for while doing the reading.
Next, I lead students in the reading by using the strategy of popcorn reading. To learn more about this strategy look at my reflection.
As students read I have them pause after the first page to try to see if they can answer any questions so far. I then have them continue for the rest of the article and have them then try to finish answering the questions.
This is a copy of the article with the places where students should find the answers and here is a copy of an answer key for the questions.
This is a copy of one student's responses to the questions.
Explain
In this section of the lesson I explain the goal of the lab to students and then review what they will be doing at each station.
- I begin by passing out the Water quality lab paper to students.
- I then have students take a few minutes (2-3) to read over the lab to themselves.
- Next, I review the goal of the lab with students in terms of testing the tapwater and rainwater so that they can come up with differences between them. I explain that they will be performing 7 different tests, and how they will be using a standard for 4 of the stations. I explain that standard is used to show what a positive result looks like. This is a video of me doing this.
- I then go through each station with students explaining to them how to use the equipment and any safety concerns.
- For station #1 they are using a dissolved oxygen probe and testing it with tap water in rain water, and distilled water. I make sure to remind them to rinse the probe between solutions. This is a picture of station 1.
- For station #2 they are using a turbidity sensor probe with a vial in which they put distilled water, rain water, and then tap water. I make sure to tell them to rinse the vial in between substances. This is a picture of station 2.
- For station #3 students use a pH probe to test tap water, rain water, and distilled water. I remind them to rinse the pH probe between solutions. This is a picture of station 3.
- For station #4 students are testing for calcium ion so I tell them to make sure to test each of the solutions as well as the standard. I also tell them to make sure to rinse the well plate when they are done. This is a picture of station 4.
- For station #5 students are testing for iron (III) chloride. This is a picture of station 5.
- For station #6 students are testing for chloride ion.
- For station #7 students are testing for sulfate ion. This is a picture of station 7.
- Finally, I break students into cooperative groups and have them go up to their first station. I make sure to have them switch roles within their cooperative groups every time that they rotate to a new station. For more details on how I do this see my reflection.
Elaborate
In this section of the lab students are doing the lab. I have them start at one station according to the cards that they recieved to make their cooperative group, and then have them rotate every 5 minutes to a new station. To keep track of time I use the tool TimerTools or you can use an online timer as well.
At each station students are expected to read the test information, perform the specified test, and then record their data.
As students are working I walk around to make sure that they are working well as a group, staying on task, and looking for differences between the tap water and rainwater. This is a movie which shows me doing this with a group of students.
Evaluate
When students are done with their labs I grade them for completion. I check that they have recorded data for all parts of the lab and have a conclusion where they write about the similarities and differences between tap water and rainwater. I grade them using a check system. Students earn a check (100%) if it is all complete (like the two examples below), a check minus (75%) if it is incomplete in terms of the comparison, and a check minus minus (50%)
These are two examples of graded labs.
In this first example, water quality lab student 1, the student simply listed the results of the tests but did not really discuss what it meant if the test was "positive" or clear in terms of that it contained chloride ions, etc.
In this second example, Water quality lab student 2, the student did a good job of explaining the difference between rainwater and tap water in terms of each of the tests.
For the most part students did well on the lab portion of the assignment in terms of gathering data, but I had varied levels of completion in regards to student conclusions. Some students did not write much in their conclusions in regards to the differences in water quality of rainwater and tap water, some students did not quite understand what a positive test meant, like in the first student example, finally some students did a great job explaining the differences as in the second student example.