5-8

E8: Demonstrate the law of Conservation of Matter.

Curriculum Organizing Questions	What does it mean to "conserve" mass? In this particular reaction, is mass being conserved? How can you measure the conservation of matter in this reaction?
Elaboration	The Conservation of Matter is really the conservation of MASS (or weight). Conservation of mass should be experienced under as many and diverse situations as possible, including physical and chemical changes. Teachers need to be careful in choosing or helping students chose) closed systems for their examples. This is a good opportunity to solidify the idea of open and closed systems and have students design their own experiments.
Specific Ideas	No matter how substances within a closed system interact with one another, or how they combine or break apart, the total weight of the system remains the same. Benchmarks 4D7 The idea of atoms explains the conservation of matter: if the number of atoms stays the same no matter how they are arranged, then their total mass remains the same. Benchmarks 4D7 When similar investigations give different results, the scientific challenge is to judge whether the differences are trivial or significnt, and it often takes further studies to decide. Benchmarks 1A1 What people expect to observe often affects what they actually do observe. Scientists know about this danger and take steps to try and avoid it when designing experiments and examining data. Benchmarks 1B3 At this level, students need to become more systematic and sophisticated in conducting their investigations … This means closing in on an unerstanding of what constitutes a good experiment. Benchmarks p. 12
Developmental & Instructional Implications	The word "conservation" has other meanings - students often believe that "conserving" something means to "make it last", like land conservation. The idea that real, visible, lasting changes can occur while mass is conseved may be difficult. See next note. (Preview Committtee) Several studies have shown that the way in which the pupils perceive a chemical or physical change may determine whether or not they regard material substance as being conserved during that change. For example, if their view of a particular change is dominated by the disappearance of some material(s), then pupils are unlikely to conserve the mass. Driver p. 77 Until the 17th C., chemists did not consider mass to be a particularly important property of matter (more than color or reactivity). In a simialr fashion, students may not focus their attention on the signficance of mass (or weight) in the conservation of matter. (Preview Committee) Students should see a great many examples of reactions that produce new substances very different from the reactants. Then they can begin to absorb the rudiments of atomic/molecular theory, being helped to see that the value of the notion of atoms lies in the explanations it provides for a wide variety of behavior of matter. Benchmarks p. 78
Examples	Reactions in baggies can be used to show conservation of mass safely and quickly.

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