This lesson is inspired by the work done by educators at the Edgerton Center at MIT, where they use LEGO pieces to teach students about chemical reactions.
I will use LEGO pieces as a tangible way to experience Law of Conservation of Matter, which is abstract and difficult to grasp with out a model.
My student goals include:
1.) I want them to have multiple ways to explain the idea of matter conservation (LEGOs, Simulation with sandwich parts, and simulation with models of molecules and atoms).
2.) I want them to see that what goes into a reaction, comes out, and that the most basic structure, such as pieces of bread and cheese--which model atoms and molecules--come out on the other side of the reaction.
Assessment boundary: Nothing will be covered about bonding of atoms and molecules. My students need to grasp the idea that matter is neither created nor destroyed, it only changes forms, so bonding doesn't matter right now. I am not concerned about misconceptions about bonding, because they will get more of that information in high school.
Giving students a solid foundation of conservation of matter will help my students when they are learning about energy and conservation of energy. In particular, when we study chemical changes, students can go back to the LEGO activity to see that when molecules break apart chemical energy can become available.
Prior to beginning this lesson, it is important that I get a sense of what my students already think or know coming in, so that I can identify common misconceptions. Once misconceptions are identified, I can plan to raise questions during class with individual students to challenge their views. The alternative of not addressing the misconceptions is that students continue to progress through science, skewing their view of how nature works.
I first ask students to explain what a chemical reaction was.
Common trends that I saw in student responses to this included:
1) "Fizzing must occur for a reaction to take place."
2) "Something new is made."
3) "Explosions happen."
These weren't necessarily incorrect, but they didn't represent deep conceptual understanding of the interactions of matter during a reaction. In particular, the interactions that result in new molecules and arrangements of matter that are derived from the original reactants.
Next, I want students to have a way to track their thoughts as they progressed through the unit, so I utilize a KLEWS chart. The KLEWS chart is them stapled into student notebooks and they periodically check back to update it as a homework assignment or, better yet, independently. Now that students have been using the KLEWS chart in class, they understand that updating it independently is an important part of the learning process.
The question on the KLEWS chart reads:
Can we create more matter or destroy matter that we already have?
I chose the Law of Conservation of Matter to anchor student understanding of how matter works. Students will develop an understanding over time that matter is not created or destroyed and this lesson sets out to help develop that idea with the concrete use of LEGOs and, later, with the PhET simulation. Regardless of the activity in the successive lessons, it's important for students to relate their experiences back to this question. Ultimately, students will create a Claims-Evidence-Reasoning statement to defend this question. The evidence collected form their research and investigations will be utilized to defend their claim, estblishing solid evidence-based argumentation abilities that are emphasized in Science and Engineering Practice 1 (Engaging in argument from evidence).
My intention of having students use LEGO blocks first is to provide a concrete experience that we can refer back to as we learn about matter conservation and chemical reactions.
To begin I prepare 6 LEGO kits that look like this.
I place each one in a small bin that is handed out to each group. I then ask each group to observe each of the separate LEGO arrangements and record their observations in the evidence column of their KLEWS chart.
Students work together to create new structures from the initial structures. They continue to record their new structures in their KLEWS chart, drawing the shapes and labeling the colors of each piece. The point of this activity is to establish the anchor experience for them to refer back to later. In that, they will begin to make connections in the next activity using the PhET simulation, especially when they realize that the number of atoms on the reactant side is the same as the amount of the same types of matter on the product side.
The get students to start making connections, I ask students to compare and contrast with their groups the similarities and differences between the initial structures and the new ones. Here are some of the common takeaways from the class discussion that ensues:
1.) Whatever is part of the original structures becomes part of the new structures, they are just rearranged.
2.) Some students even make the connection that nothing is removed (destroyed), it's just rearranged.
Students record comments from the class discussion in their notebooks.
Now that student have experienced and reflected on this anchor activity, it is time for them to delve a little deeper with the use of this PhET simulation.
Using this simulation, students will collect evidence that will lead to a deeper understanding of chemical reactions and matter conservation. I begin by reviewing how to navigate the simulation and the general set-up of the reactants and products. I state: "This is similar to the LEGO activity, only this is an online version that more accurately resembles what is going on during a reaction. The left hand side (reactants) represents the initial LEGO pieces, while the right hand side (products) represents the new structures that you made. To begin, we let's practice what we are going to do with the sandwich simulation. In this part, you have to put the correct amount of each piece, in order to create the sandwiches (products)."
As students go through this process, I require them to record pictures of the reactants vs. the products, similar to the LEGO activity when they drew the before and after pictures. I then explain that they will then move onto the next part of the activity which deals with molecules and atoms. Students will again perform the same task of drawing what they see on both sides. My goal this year, while teaching lessons more aligned with the NGSS, was to make phenomena more visual. This lesson emphasizes the importance of visual thinking to build deep conceptual understanding of the topic. Students can either record their evidence on the KLEWS chart, or place a note that states what pages in their science notebook contain their observations and comments.
Upon completing the first two parts of the simulation, sandwiches and molecules, students can challenge themselves by playing the game portion of the simulation. The game feature is great because it has students "balance" both sides of the reaction, reiterating the idea that matter is not created or destroyed. A particularly poignant aspect of the game is that it gives students the products and they have to pick--using the drop down arrows--the correct number of reactants.
Here is a student working through the game portion of the simulation.
I am checking for understanding in 2 ways:
1) I am circulating from group-to-group during the lesson and asking probing questions, like "What are you noticing from the simulation?" or "Are there any patterns that you're seeing in terms of the number of atoms on one side, compared to the other side of a reaction?"
2) I assign a 3-circle Venn Diagram to my students for HW. I ask them to compare and contrast the three important aspects of today's lesson:
How are the LEGO activity, Sandwich part of the simulation and Molecule part of the PhET simulation similar yet different?
We then review the Venn Diagram the next class to clarify meaning and activate prior knowledge.