Are students reflecting on what their calculated values indicate? This question constantly runs through the minds of chemistry teachers across the country. Recently educators have seen shifts in instruction that promote connections to real-world phenomena using conceptual depth in understanding. From Modeling Instruction to Target Inquiry, Advanced Placement to Consumer Chemistry, all our students are required to justify their responses. Although educators are revising their approach the question still remains, are the students comprehending what their data represents?

For introductory chemistry students, stoichiometry tends to be the pivotal concept that challenges them to reflect on their calculated data in particulate manner. Students tend to memorize the order to use various ratios however at the end of the unit they may not have an understanding of how each ratio related to one another as well as how the data relates to the system in question.

Every chemistry teacher has their favorite stoichiometry lab, for me it is the Nail Lab in which students react a copper (II) chloride solution with an iron nail to investigate the relationships between the amount of iron reacted, the amount of copper produced, and the meaning of the balanced chemical equation coefficients. However, after the lab another example should be provided so students can continue to make connections between the conservation of mass and stoichiometry ratios.

A companion resource that could be used during this unit is the Conservation of Mass video from the STEM Concept Video Series produced by the Teaching and Learning Laboratory at the Massachusetts Institute of Technology. This video along with the companion Instructor’s Guide, provides educators with an opportunity to connect prior knowledge, of open and closed systems as well as stoichiometry calculations, to additional real world situations besides the ones identified in previous laboratory experiments in the classroom.

With the completion of the video, educators can continue with an extension activity such as a discussion about verbalizing mole ratios to develop justification of what occurred in each scenario. Another follow up exercise is to have students reflect on the misconceptions that tend to occur when individuals try to explain these two real-world situations. Students could view the Veritasium video “Where do Trees Get Their Mass From?” or a brief clip from “Lessons from Thin Air” from the Minds of Our Own video series produced by the Harvard-Smithsonian Center for Astrophysics. Regardless of the exercise chosen, the objective is to have the students reflect and find meaning in the values they calculated for this content and beyond.

References

M.I.T: Teaching and Learning Laboratory- STEM Concept Videos - http://tll.mit.edu/help/stem-concept-videos

Minds of Our Own Documentary: Lessons from Thin Air - http://www.learner.org/vod/vod_window.html?pid=77

Veritasium: Where do Trees Get Their Mass From? https://www.youtube.com/watch?v=2KZb2_vcNTg

## NGSS

Students who demonstrate understanding can use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

*More information about all DCI for HS-PS1 can be found at https://www.nextgenscience.org/dci-arrangement/hs-ps1-matter-and-its-interactions and further resources at https://www.nextgenscience.org.

Students who demonstrate understanding can use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

Assessment does not include complex chemical reactions.

Emphasis is on using mathematical ideas to communicate the proportional relationships between masses of atoms in the reactants and the products, and the translation of these relationships to the macroscopic scale using the mole as the conversion from the atomic to the macroscopic scale. Emphasis is on assessing students’ use of mathematical thinking and not on memorization and rote application of problem - solving techniques.