Unit Overview – Buoyancy and Density

The big picture stuff:

Currently, California formally introduces physical and chemical changes in grade 5. The NGSS introduces physical changes like heating and cooling in grade 2 and chemical changes in grade 5 (PS1B). At this level, the goal is for students to answer the questions,“What happens when new materials are formed? What stays the same and what changes?” by understanding what occurs at the atomic and molecular scale during chemical reactions. By the end of middle school, students will be able to provide molecular level accounts to explain that chemical reactions involve regrouping of atoms to form new substances and that atoms rearrange during chemical reactions. Students are also able to apply an understanding of the design and the process of optimization in engineering to chemical reaction systems.

Next Generation Science Standards – Middle School (NGSS-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. Assessment boundary includes analysis of melting points, boiling points, solubility, flammability and odor.

Explanation: Each pure substance has characteristic physical and chemical properties(for any bulk quantity under given conditions) that can be used to identify it.

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.

Emphasize: law of conservation of matter, on physical models or drawings, including digital forms, that represent atoms. Do not include the use of atomic masses, balancing symbolic equations, or intermolecular forces.

Core ideas: Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants. The total number of each type of atom is conserved, and thus the mass does not change.

PS1-6. Undertake a design project to construct, test, and modify a device that either releases or absorbs thermal energy by chemical processes.

Emphasize: design, controlling the transfer of energy to the environment, and modification of a device using factors such as type and concentration of a substance. Examples: Designs could involve chemical reactions such as dissolving ammonium chloride or calcium chloride. Focus on the criteria of amount, time, and temperature of substance in testing the device.

Core ideas: Some chemical reactions release energy, others store energy.

ETS1.B: Developing Possible Solutions

Core ideas: A solution needs to be tested, and then modified on the basis of the test results, in order to improve it.

ETS1.C: Optimizing the Design Solution

Core ideas: Although one design may not perform the best across all tests, identifying the characteristics of the design that performed the best in each test can provide useful information for the redesign process—that is, some of the characteristics may be incorporated into the new design. The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution.

Science and Engineering:

• Analyze and interpret data to determine similarities and differences in findings.
• Science knowledge is based upon logical and conceptual connections between evidence and explanations.
• Develop a model to describe unobservable mechanisms.
• Undertake a design project, engaging in the design cycle, to construct and/or implement a solution that meets specific design criteria and constraints.

Crosscutting concepts:

• Macroscopic patterns are related to the nature of microscopic and atomic-level structure.
• Matter is conserved because atoms are conserved in physical and chemical processes.
• The transfer of energy can be tracked as energy flows through a designed or natural system.

California Science Standards:

Physical Science Standards:

3d. Students know the states of matter (solid, liquid, gas) depend on molecular motion.

3e. Students know that in solids the atoms are closely locked in position and can only vibrate; in liquids the atoms and molecules are more loosely connected and can collide with and move past one another; and in gases the atoms and molecules are free to move independently, colliding frequently.

5a. Students know reactant atoms and molecules interact to form products with different chemical properties.

5b. Students know the idea of atoms explains the conservation of matter: In chemical reactions the number of atoms stays the same no matter how they are arranged, so their total mass stays the same.

5c. Students know chemical reactions usually liberate heat or absorb heat.

5d. Students know physical processes include freezing and boiling, in which a material changes form with no chemical reaction.

Investigation and Experimentation Standards:

9a. Plan and conduct a scientific investigation to test a hypothesis.

9b. Evaluate the accuracy and reproducibility of data.

9c. Distinguish between variable and controlled parameters in a test.