HS-PS1-7 | Conservation of Mass

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

Clarification statement: 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.

Assessment boundary: Assessment does not include complex chemical reactions.

Assessment

What assessment of HS-PS1-7 might look like on a NY state exam.

Exam	Cluster	Question
August 2026	Electricity Generation in New York State	Question 3
	The Fruit Industry in New York State	Question 8
	The ABCs of Ultraviolet Radiation	Question 29
	Catalytic Converter in Cars	Question 31
June 2026	Chemistry of Beverages	Question 6
	The Accidental Development of Breathable, Waterproof Fabric	Question 15
	Balloon Arches	Question 24
	Chip Bag: PFAS vs PLA Plastics	Question 33
Sample clusters (Spring 2025)	Smartphone Chemistry	Question 3
	A Profitable Blueberry Field	Question 4
	A Profitable Blueberry Field	Question 5

Performance Level Descriptions

PLDs communicate the knowledge and skills expected of students to demonstrate proficiency in each Learning Standard. NYS assessments classify student performance into one of five levels.

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Level 1: Use information provided to identify mathematical representations that demonstrate atoms and/or mass are conserved during a chemical reaction.

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Level 2: Use or complete a mathematical representation to demonstrate that atoms and/or mass are conserved during a chemical reaction.

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Level 3: Construct a mathematical representation and/or calculate a quantity (e.g. # of particles, volume of a gas, etc.), using the relationship that atoms and/or mass are conserved during a chemical reaction.

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Level 4: Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

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Level 5: Create and revise mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

Resources

Examples and discussion of resources for the learning, teaching, and assessment of HS-PS1-7.

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NGSS Dimensions

Performance expectation HS-PS1-7 was developed using the following elements from the NRC document A Framework for K-12 Science Education:

Science and Engineering Practices

• Using Mathematics and Computational Thinking
  • Use mathematical representations of phenomena to support claims.

Disciplinary Core Ideas

• 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.

Crosscutting Concepts

• Energy and Matter
  • The total amount of energy and matter in closed systems is conserved.

Page contributors: Conrad Richman, Caroline Leonard

Chemistry | HS. Chemical Reactions