Highly Recommended
Like all our Science Reasoning Center activities, the completion of Stoichiometry relies on the use of provided information about a phenomenon, experiment, or data presentation to answer questions. This information is accessible by tapping on the small thumbnails found on the bottom right of every question. However, it may be considerably easier to have a printed copy of this information or to display the information in a separate browser window. You can access this information from this page

The Standards
The Stoichiometry activity is an NGSS-inspired task that consists of five activities that center around the concept of atom and mass conservation. Calculations are involved but the answers are not ends in themselves. The role of all calculations is to demonstrate that the concept that if atoms are conserved in a chemical reaction, then it makes sense that mass is conserved. This concept is approached from a variety of angles. Every calculation is accompanied by a follow-up, sense-making question. The activity aligns with the HS-PS1-7 performance expectation of the Next Generation Science Standards.

This NGSS-inspired task consists of five parts. Each part involves a different type of skill or understanding. Collectively, the five parts were designed to address the following NGSS performance expectation:

HS-PS1-7:
Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

As a whole, the questions in this task address a wide collection of disciplinary core idea (DCI), crosscutting concepts (CCC), and science and engineering practices (SEP). There are 28 multi-part questions organized into 12 Question Groups and spread across the five activities. Each question is either a 2D or (preferably) a 3D question. That is, the task of answering the question requires that the student utilize at least two of the three dimensions of the NGSS science standards - a DCI, a CCC, and/or an SEP.

The following DCI, SEPs, and CCCs are addressed at some point within Stoichiometry:

DCI:  PS1.B: Chemical Reactions
• The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

SEP 2.6:  Developing and Using Models
Develop and/or use a model (including mathematical and computational) to generate data to support explanations, predict phenomena, analyze systems, and/or solve problems.

SEP 5.3:  Using Mathematics and Computational Thinking
Use mathematical, computational, and/or algorithmic representations of phenomena or design solutions to describe and/or support claims and/or explanations.

SEP 6.2:  Constructing Explanations and Designing Solutions
Construct and revise an explanation based on valid and reliable evidence obtained from a variety of sources (including students’ own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future.

SEP 6.3:  Constructing Explanations and Designing Solutions
Apply scientific ideas, principles, and/or evidence to provide an explanation of phenomena and solve design problems, taking into account possible unanticipated effects.

SEP 7.4:  Obtaining, Evaluating, and Communicating Information
Construct, use, and/or present an oral and written argument or counter-arguments based on data and evidence.

CCC 1.1: Patterns
Patterns of performance of designed systems can be analyzed and interpreted to reengineer and improve the system.

CCC 3.1: Scale, Proportion, and Quantity
The significance of a phenomenon is dependent on the scale, proportion, and quantity at which it occurs.

CCC 4.1: Systems and System Models
When investigating or describing a system, the boundaries and initial conditions of the system need to be defined and their inputs and outputs analyzed and described using models.

CCC 5.2: Energy and Matter
The total amount of energy and matter in closed systems is conserved.

CCC 7.1: Stability and Change
Much of science deals with constructing explanations of how things change and how they remain stable.

Here is our NGSS-based analysis of each individual activity of the Stoichiometry Science Reasoning task. The core ideas, crosscutting concepts, and science and engineering practices that we reference in our analysis are numbered for convenience. You can cross-reference the specific notations that we have used with the listings found on the following pages:

#### Part 1:  Paragraph Completion

This activity involves two paragraph-completion exercises. Students use a word/phrase bank to select missing words and phrases in order to complete a paragraph. The paragraphs focus on the mathematical relationships between atomic scale quantities and macroscopic scale quantities. There are two such paragraphs; one contains 8 blanks and the other contains 9 blanks. Once students complete their paragraph, they can submit their answers for evaluation and feedback. On each answer submission, they are told the number of correct blanks but not told which blanks are correct. Students have an unlimited number of opportunities to correct their answers. Students earn the Trophy for the activity once they correctly complete both paragraphs.

NGSS Claim Statement: Use principles associated with chemical reactions to explain the mathematical relationships between atomic scale quantities and macroscopic scale quantities.

 Target DCI(s) Target SEP(s) Target CCC(s) Chemical Reactions PS1.B The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions. Constructing Explanations and Designing Solutions SEP 6.3 Apply scientific ideas, principles, and/or evidence to provide an explanation of phenomena and solve design problems, taking into account possible unanticipated effects. Using Mathematics and Computational Thinking SEP 5.3 Use mathematical, computational, and/or algorithmic representations of phenomena or design solutions to describe and/or support claims and/or explanations. Energy and Matter CCC 5.2 The total amount of energy and matter in closed systems is conserved. Patterns CCC 1.1 Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena.

#### Part 2: Elemental Measures (a.k.a., Stoikheion + Metry)

This activity consists of three multi-part calculation problems. Each problem is separated into an atomic scale analysis (the numbers of atoms of each element are determined) and a macroscopic scale analysis (moles or mass of each element are determined). The three problems increase in sophistication from two elements, to three elements, and finally to four elements involved in the reaction. Each problem finishes with a forced-choice question regarding atoms and mass being conserved. If a calculated answer is incorrect, it is identified and students are permitted to try again until it is correct. Students earn the Trophy for the activity when they demonstrate mastery of all three problems.

NGSS Claim Statement: Perform calculations of the initial and final amounts of atomic scale and macroscopic scale quantities in order to demonstrate that atoms, and therefore mass, are conserved in chemical reactions.

 Target DCI(s) Target SEP(s) Target CCC(s) Chemical Reactions PS1.B The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions. Using Mathematics and Computational Thinking SEP 5.3 Use mathematical, computational, and/or algorithmic representations of phenomena or design solutions to describe and/or support claims and/or explanations. Developing and Using Models SEP 2.6 Develop and/or use a model (including mathematical and computational) to generate data to support explanations, predict phenomena, analyze systems, and/or solve problems. Energy and Matter CCC 5.2 The total amount of energy and matter in closed systems is conserved. Patterns CCC 1.1 Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena.

#### Part 3: Mass Conservation

This activity consists of two multi-part calculation problems. In the first problem, students perform several mole-to-mole conversions. Then they determine the number of moles of atoms of every element before and after the reaction. They draw a conclusion based on their results. In the second problem, students perform several gram-to-gram conversions. Then they determine the number of grams of every element before and after the reaction. Once more they draw a conclusion based on their results. Like the entirety of this activity, if a calculated answer is incorrect, it is identified and students are permitted to try again until it is correct. Students earn the Trophy for the activity when they demonstrate mastery of both problems.

NGSS Claim Statement: Use mathematical calculations to generate data to support a conclusion for a closed system at both the atomic and the macroscopic scale that atoms, and therefore mass, are conserved in a chemical reaction.

 Target DCI(s) Target SEP(s) Target CCC(s) Chemical Reactions PS1.B The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions. . Using Mathematics and Computational Thinking SEP 5.3 Use mathematical, computational, and/or algorithmic representations of phenomena or design solutions to describe and/or support claims and/or explanations. Developing and Using Models SEP 2.6 Develop and/or use a model (including mathematical and computational) to generate data to support explanations, predict phenomena, analyze systems, and/or solve problems. Energy and Matter CCC 5.2 The total amount of energy and matter in closed systems is conserved. Systems and System Models CCC 4.1 When investigating or describing a system, the boundaries and initial conditions of the system need to be defined and their inputs and outputs analyzed and described using models.

#### Part 4: Chemistry on Planet Exwizee

This activity consists of two multi-part calculation problems. In both problems, students are given the mass of a reactant and must calculate the mass of the second reactant and the mass of both products. They then determine the total mass of the system of reactants before the reaction and the total mass of the system of reactants after the reaction. They compare the total mass calculations to one another and draw a conclusion. If a calculated answer is incorrect, it is identified and students are permitted to try again until it is correct. Students earn the Trophy for the activity when they demonstrate mastery of both problems.

NGSS Claim Statement: AAA

 Target DCI(s) Target SEP(s) Target CCC(s) Chemical Reactions PS1.B The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions. Using Mathematics and Computational Thinking SEP 5.3 Use mathematical, computational, and/or algorithmic representations of phenomena or design solutions to describe and/or support claims and/or explanations. Developing and Using Models SEP 2.6 Develop and/or use a model (including mathematical and computational) to generate data to support explanations, predict phenomena, analyze systems, and/or solve problems. Energy and Matter CCC 5.2 The total amount of energy and matter in closed systems is conserved. Systems and System Models CCC 4.1 When investigating or describing a system, the boundaries and initial conditions of the system need to be defined and their inputs and outputs analyzed and described using models.

#### Part 5: Unlawful and Lawful Chemistry

This activity consists of two multi-part calculation questions with a paragraph completion follow-up question. Given the mass of a reactant in a synthesis reaction, students calculate the mass of the other reactant, the mass of the product, and the total mass or reactants and of products. They perform the calculations for a situation in which the reaction is incorrectly balanced (unlawful chemistry) and for the same reaction when it is balanced (lawful chemistry). For both situations, they compare the total mass of reactants to the total mass of products and make a conclusion. They then complete a paragraph that summarizes their findings. When a calculation or paragraph blank is missed, students have opportunity to correct the errors; there is no limit on how many corrections are allowed.  Students earn the Trophy for this activity once they demonstrate mastery on all three questions.

NGSS Claim Statement: Use mathematical calculations to generate data to support a conclusion that for a closed system at the macroscopic scale atoms, and therefore mass, are conserved in a chemical reaction.

 Target DCI(s) Target SEP(s) Target CCC(s) Chemical Reactions PS1.B The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions. Using Mathematics and Computational Thinking SEP 5.3 Use mathematical, computational, and/or algorithmic representations of phenomena or design solutions to describe and/or support claims and/or explanations. Engaging in Argument from Evidence SEP 7.4 Construct, use, and/or present an oral and written argument or counter-arguments based on data and evidence. Constructing Explanations and Designing Solutions SEP 6.2 Construct and revise an explanation based on valid and reliable evidence obtained from a variety of sources (including students’ own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future. Energy and Matter CCC 5.2 The total amount of energy and matter in closed systems is conserved. Systems and System Models CCC 4.1 When investigating or describing a system, the boundaries and initial conditions of the system need to be defined and their inputs and outputs analyzed and described using models.

Complementary and Similar Resources
The following resources at The Physics Classroom website complement the Stoichiometry Science Reasoning Activity. Teachers may find them useful for supporting students and/or as components of lesson plans and unit plans.

Concept Builders, Chemistry - Molar Mass

Concept Builders, Chemistry - Molar Conversions

Concept Builders, Chemistry - Stoichiometry: Math Relationships

The Calculator Pad, Stoichiometry, Problem Sets 1 - 16