MS-PS1-5 | Conservation of Matter
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 the 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.
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 four levels.
Resources
Examples and discussion of resources for the learning, teaching, and assessment of MS-PS1-5.

Assessment
What assessment of MS-PS1-5 might look like on a NY state exam.
NGSS Dimensions
Performance expectation MS-PS1-5 was developed using the following elements from the NRC document A Framework for K-12 Science Education:
- Developing and Using Models
- Develop a model to describe unobservable mechanisms.
- PS1.B: Chemical Reactions
- (NYSED) Substances react chemically in characteristic ways. When substances react, the atoms that make up the molecules rearrange, forming new substances with different properties.
- The total number of atoms does not change in a chemical reaction and thus mass is conserved.
- Energy and Matter
- Matter is conserved because atoms are conserved in physical and chemical processes.