Controlling the Amount of Products in a Chemical Reaction

Contributor
American Chemical Society
Type Category
Instructional Materials
Types
Activity , Demonstration , Model
Note
This resource, vetted by NSTA curators, is provided to teachers along with suggested modifications to make it more in line with the vision of the NGSS. While not considered to be “fully aligned,” the resources and expert recommendations provide teachers with concrete examples and expert guidance using the EQuIP rubric to adapted existing resources. Read more here.

Reviews

Description

This activity begins with an analysis of the chemical equation for the reaction between vinegar and baking soda.  Students try this reaction on their own, experimenting with how changing the amount of one or more of the reactants affects the amount of products.  Students analyze a molecular model to follow the number and type of atoms from reactants to products. Through experimentation and discussion, students are asked to make connections between the written chemical equation, the molecular model, and the real substances in the reaction.  This lesson includes digital images, a student reading, and a detailed teacher’s guide.

Intended Audience

Educator and learner
Educational Level
  • Middle School
Language
English
Access Restrictions

Free access - The right to view and/or download material without financial, registration, or excessive advertising barriers.

Performance Expectations

MS-PS1-5 Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.

Clarification Statement: Emphasis is on law of conservation of matter and on physical models or drawings, including digital forms, that represent atoms.

Assessment Boundary: Assessment does not include the use of atomic masses, balancing symbolic equations, or intermolecular forces.

This resource is explicitly designed to build towards this performance expectation.

Comments about Including the Performance Expectation
Students are not creating their own model, but are using the model on both the digital images and the student sheet to count the number of atoms in both the reactants and products to explicitly show the Law of Conservation of Matter. The digital model used matches the graphics on the student sheet. Having students shade in their paper to color code the atoms (especially to match the colors used on the digital imaging) helps students to visualize the rearrangement of atoms.

MS-PS1-2 Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.

Clarification Statement: Examples of reactions could include burning sugar or steel wool, fat reacting with sodium hydroxide, and mixing zinc with hydrogen chloride.

Assessment Boundary: Assessment is limited to analysis of the following properties: density, melting point, boiling point, solubility, flammability, and odor.

This resource is explicitly designed to build towards this performance expectation.

Comments about Including the Performance Expectation
Students are experimenting with controlling the amount of products by the amount of reactants used and are building towards this PE. The lesson specifically asks students to tell whether a chemical reaction occurred and what evidence they have during the baking soda and vinegar demonstration and during the alka-seltzer culminating activity. They are using the amount of production of a gas (carbon dioxide) to fill a graduated cylinder and are trying to determine the ideal amounts of each reactant to do this. When students add too much of one of the reactants, such as a mountain of baking soda, seeing the unreacted materials is a good learning moment for students to connect to this PE. The teacher should ask the group(s) about what happened during the discussion. Sharing out the data tables before explaining what is happening with the molecules is a good way to directly address the analysis part of this PE, as students can discuss the multiple ways they were able to reach the top of the graduated cylinder and discuss what this means.

Science and Engineering Practices

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
Students experiment with different amounts of reactants to create the ideal amount of foam to fill the graduated cylinder. They record the possible combinations on page 538 of the student sheet. While students are working, asking them to explain their next steps will give them a chance to discuss their findings so far. Having groups share these findings and discuss them makes this process more explicit, especially to compare the multiple successful combinations students tried. Some groups may not be successful, so comparing their data table may show them how close they were to a successful result.

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
Students count the number and type of atoms in the reactants and products in both a data table and in a molecular model. They experiment with the amounts of reactants and how much product is created, but cannot observe this at the molecular level without the model, both on their paper and on the projector as a digital image. Using this model helps to make sense of why you can’t just continue to add more of one reactant without also adding the other. Pointing out a group who had a pile of unreacted baking soda may help when doing the Explaining it with Molecules portion of the lesson.

Disciplinary Core Ideas

This resource is explicitly designed to build towards this disciplinary core idea.

Comments about Including the Disciplinary Core Idea
Students count the number and type of atoms in the reactants and products in both a data table and in a molecular model. They experiment with the amounts of reactants and how much product is created, but cannot observe this at the molecular level without the model, both on their paper and on the projector as a digital image. Using this model helps to make sense of why you can’t just continue to add more of one reactant without also adding the other. Pointing out a group who had a pile of unreacted baking soda may help when doing the Explaining it with Molecules portion of the lesson.

Crosscutting Concepts

This resource is explicitly designed to build towards this crosscutting concept.

Comments about Including the Crosscutting Concept
This lesson and the accompanying visual aids help students to trace the number and type of atoms from reactants to products to show the Law of Conservation of Matter. Throughout the unit of lessons, a balance is used to visualize this idea. Question 3 on page 537 of the student sheet specifically asks about how mass is conserved. Spending the time to discuss students’ ideas about this will help to reinforce this concept.

Resource Quality

  • Alignment to the Dimensions of the NGSS: The learner engages with controlling the amount of product in a reaction to demonstrate the Law of Conservation of Matter in all three dimensions. Students try to solve the problem of producing the right amount of foam and then analyze their data and make connections to what is happening at the molecular level. Students use a model through a digital image to trace the number and type of atoms throughout the reaction, however, the models are not student-created. One way to make this lesson stronger might be a follow-up where students create their own manipulative models to build the molecules to trace the atoms from reactant to product. This lesson does build students to the understanding to make these models themselves.

  • Instructional Supports: This lesson provides students the opportunity to discuss their data in the multiple ways groups could produce the ideal amount of foam. The data table provides students with evidence to justify their findings. This lesson also provides support in all three dimensions, helping students to connect their experimental data with the Law of Conservation of Matter with the use of both data tables and modeling. The multiple modalities provided in this lesson, as well as the accompanying student reading, provides some differentiation for the learner in need of additional support. The extension activity with citric acid could be made more challenging by asking students to create their own molecular model to prove this additional experiment demonstrates the Law of Conservation of Matter. As it stands, it is only a demonstration. If materials were readily available, students already meeting the performance expectation could experiment with the amounts of the reactants in this extension experiment.

  • Monitoring Student Progress: This lesson offers several 3D formative assessment opportunities. As stated previously, asking students to create or build upon the models given would help to strengthen student understanding. However, simply using the models given does help to foster understanding with following the atoms from reactant to product and reinforces the rearrangement. Student data tables tracing the number and type of atoms from reactants to products helps to gauge student understanding of both the PE, DCI, and CCC associated with the Law of Conservation of Matter, describing how the total number of atoms in a reaction does not change. The answer key provides examples of possible student responses to help the teacher. The questions asked, both suggested for discussion and in the student sheet, offer students meaningful opportunities to explain their reasoning, such as “Why, on the molecular level, does changing the amount of baking soda or vinegar affect the amount of carbon dioxide gas produced?” Discussing these questions as a class after students complete on their own or in a small lab group would help students to continue to justify their work and strengthen their understanding.

  • Quality of Technological Interactivity: This lesson has little technological interactivity. The digital images are to be projected to the class, not interacted upon by students.