Science - 5th Grade
Standard 1 Objective 1
1 class periods of 60 minutes each
The Law of Conservation of Mass states that mass is conserved in physical and chemical changes. Students explore this concept by taking initial masses, making predictions, and finding final masses of physical and chemical changes. Students observe water changing from ice to a liquid, a piece of cardboard being cut up, salt dissolving in water, Alka-Seltzer reacting in water, and water's physical property of cohesiveness being disrupted by soap.
These are the supplies needed for each group.
Matter is anything that takes up space and has mass. Matter is composed of atoms and molecules and is always changing its form by either physical or chemical changes. The Law of Conservation of Mass states that mass is neither created nor destroyed during any physical or chemical changes.
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.
1a. Observe simple objects, patterns, and events and report their observations.
1c. Given the appropriate instrument, measure length, temperature, volume, and mass in metric units as specified.
1d. Compare things, processes, and events.
1h. Predict results of investigations based on prior data.
1i. Use data to construct a reasonable conclusion.
2e. Seed and weigh evidence before drawing conclusions.
3a. Know and explain science information specified for the grade level.
4a. Record data accurately when given the appropriate form.
4c. Use scientific language in oral and written communication.
6c. Science findings are based upon evidence.
Pre-lab discussion: Define matter, and physical and chemical changes. Demonstrate a physical change for the students. Some ideas are: crumpling paper, using instant snow (Stevespanglerscience.com Item #: WFXS-100, $6.99), or crushing a can. Discuss a chemical change such as burning a log or frying an egg. Explain that since the beginning of our earth, all the matter that was on the earth is simply being changed from one form to another. Whenever these changes take place there is no change in mass by either losing or gaining mass. Mass in our world is conserved. Students will observe this today when they perform several physical and chemical changes.
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.
** The bubble should collapse because soap will interfere with the cohesiveness of water and it breaks down. This is a physical change because the molecule of water didn't change just its behavior did.
** The soap rode across the top of the water and pushed the pepper to the edges. This is a physical change on the surface of the water that propelled the pepper to the side.
Rio Tinto Hands-on Science Curriculum Team