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.
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).:
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 one student's responses to the questions.
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.
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.
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.