As students enter the classroom, they take out their journals and begin working on a prompt: Should we use the PLA in the 3D printer to make a food bowl for Mo*? Why or why not? What about a water bowl?
This question is similar to one posed on the students' notes review with the exception that it requires them to explain the reasoning behind their answer. By doing this, the students have already thought about the question when they were completing an assignment and now they are being asked to revisit their thoughts and justify them with information from their notes.
*Mo is our class pet. He is a Syrian hamster and the students are very attached to him. His safety and well being are very important to the students, so they take this journal seriously.
As the students write, I circulate through the room looking at their responses so I have a better idea of how to focus the class discussion and review.
After the students have had an opportunity to respond to the prompt, I ask students to take out their notes and Polymers notes review. I have the students share their journal responses as a way to review this set of notes. I begin the review by pointing going over the definitions of monomers and polymers, using a bulletin board as a reference.
As the students share their responses, I ask them to point out information from their notes to support their idea. Several of the students were concerned that making a food bowl out of PLA would be dangerous for Mo because he would chew on it. I showed the students his current food bowl and explained that as a rodent, Mo's teeth continue to grow so it is important for him to chew on different items. I then focus the discussion toward what PLA is made from. Some of the students say that since bacteria is used to make PLA, it would not be safe. Other students then point out that it is the same bacteria used to make yogurt, and Mo particularly enjoys eating yogurt treats. Some of the students are also concerned about the corn used to make the plastic, so I pass around Mo's food bowl and show them the corn kernels that are in it. One student pointed out that while the plastic would not be harmful to Mo, there are small holes in the items we have previously constructed from the PLA and those areas could make it possible for dangerous bacteria to grow.
At this point, most of the flipped notes have been covered through the food bowl debate, but I do spend time discussing some of the benefits and drawbacks of using PLA. This discussion meets NGSS MS-PS1-3 by having students discuss how PLA, a synthetic, is made from a natural source.
This is the notes video I created for my students to view prior to this lesson.
After our review of the notes, I tell the students that we will make our own version of corn plastic to conduct experiments on. I show the students the lab activity they will be working on and review the directions with them. I also point out that there are several questions and observations they must complete while working on the lab. Before entering the lab, the students put away their journals and take out their Chromebooks. Once in the lab, I show the students where the supplies they need are located and then demonstrate how the lab is to be completed. The students then open the Making Polymers lab sheet on their Chromebooks and begin working. As the students work, I walk through the lab asking them questions about their procedure and making sure that they are following the procedures correctly. I also make sure that their initial corn plastic mixture is prepared properly. Sometimes the students do not have enough water in their initial mixture and it is too dry and clumpy, so I add water as necessary. I also microwave the plastic for the students. It is important to make sure that the plastic bag is not sealed while it is microwaved. I also take this opportunity to teach a safety lesson by asking the students to explain why the bag should not be sealed while it is heated.
The guiding questions in this portion of the lab meet NGSS standard MS-PS1-2 in which students note the qualities of a substance before and after combining items to see if a chemical reaction has taken place. The section of the lab in which the students compare the mass of the plastic reactants with the mass of the plastic products addresses NGSS SP4 as students analyze data and then we tie their conclusions back to the Law of Conservation of Mass.
Near the end of class I have the students begin to clean up their lab stations. Once the lab tables are clean, I lead a group discussion regarding the quantitative and qualitative observations made during the lab. I ask the students to describe the ingredients of the plastic before heating and then compare those observations with their observations of the plastic after heating. This provides an opportunity to discuss the small change in mass. While I have discussed this with most of the groups already, it is helpful to have a whole group discussion about what the students think happened to cause the change in mass. Some of the students will generally state that "something evaporated." I ask them to be more specific and to tell me what they think evaporated and then I ask them to explain their answer.