OpenSciEd Unit 7.1 · Lesson 12 · 12.A
Look for: Students comparing the different models to ac…
From Teacher Edition
Facilitation guidance from the lesson plan — what to notice in student thinking and how to respond while teaching.
Building towards
12.A.2 Construct an explanation for how the atoms in the molecules of the starting substances rearrange to form new products in the bath bomb, but the number and types of atoms do not change and thus mass is conserved and evaluate two different molecular models for different ratios of reactant and product molecules to determine which better supports this explanation.
What to look / listen for
Students comparing the different models to account for all the atoms in the reactants also being in the products. They should be looking for the amount of atoms as well as the type of atom.
What to do
If students are not accounting for there being the same number of atoms in both the reactants and products, ask some probing questions to remind them of what we figured out about the mass of the bath bomb when in a closed system. When they say the mass didn’t change, refer them to Comparing Molecular Ratios in a Chemical Reaction and encourage them to count up all the atoms to determine whether the same amount of matter is in the reactants as is in the products in both models.
Then bring students back together and have them share their ideas.