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Main Curriculum Tie:
Background For Teachers:
A physical change occurs when the appearance of a substance changes but its chemistry remains the same. No new substance is formed in a physical change; water moving between states of matter, a Popsicle melting, and a paper crumbled are examples of physical changes.
A chemical change occurs when bonds are broken between atoms and rearranged into new, entirely different substances such as burning a log and frying an egg.
Intended Learning Outcomes:
Instructional procedure: In this lab, precise measuring on the balance and counting of gram cubes is critical. None of the masses should change but you may have change due to errors and lack of precise equipment. This is a great discussion to have with students before you begin the lab.
Experiment I. Changing the state of water does not affect its mass.
** The mass shouldn’t change because mass is conserved in nature, changing the state of water doesn’t change its mass.
Experiment II. Physical changes in appearance do not affect mass.
** Mass is conserved in nature, changing the arrangement of parts during a physical change does not change its mass.
Experiment III. A physical change as salt is dissolved in water does not affect mass.
** The mass should not change because mass is conserved.
Experiment IV. In a chemical change, mass is again conserved.
** In this reaction we form a new substance, carbon dioxide gas, which is a chemical change. Mass is also conserved in chemical changes.
** Ask the students if we would have gotten the same mass if we didn’t seal the bag. No, because some of our matter would have escaped into the air in the form of carbon dioxide gas.
Experiment V. Observing a physical change in the properties of water.
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