HS-PS1-7 | Conservation of Mass
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.
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.
Vocabulary
Terms from the Chemistry Glossary that come from this standard or from the released exam questions that assess it.
- atom
- chemical property
- chemical reaction
- claim
- closed system
- conservation of atoms
- conservation of mass
- conversion factor
- element
- energy
- gas
- macroscopic scale
- mass
- mathematical representation
- matter
- mole
- particle
- phenomenon
- product
- properties
- proportional relationship
- reactant
- reaction
- volume
- balanced equation – Aug 2026
- bioplastic – June 2026
- bond – June 2026
- climate change – Aug 2026
- coefficient – June 2026
- complete combustion – Aug 2026
- concentration – June 2026
- conservation of matter – Aug 2026, June 2026
- criteria – June 2026
- evidence – Sample 2025
- high temperature – June 2026
- molar mass – June 2026
- molecule – June 2026
- monomer – June 2026
- oxide – Sample 2025
- pressure – June 2026
- significant figures – June 2026, Sample 2025
- solution – June 2026
- substance – June 2026, Sample 2025
- synthesis – Aug 2026
- temperature – June 2026
- Avogadro’s number – implied by "the mole as the conversion from the atomic to the macroscopic scale"
- molar volume (22.4 L/mol at STP) – implied by "calculate a quantity (e.g. # of particles, volume of a gas)"
- mole ratio – the Smartphone Chemistry rubric multiplies by "2 moles Al2O3 / 4 moles Al".
- stoichiometry – implied by "proportional relationships between masses of atoms in the reactants and the products"
- structural formula – drawn but not named in June 2026 Chip Bag Figure 1 and the June 2026 Equilibria in the Blood rubric.
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:
- Using Mathematics and Computational Thinking
- Use mathematical representations of phenomena to support claims.
- 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.
- Energy and Matter
- The total amount of energy and matter in closed systems is conserved.