MS - PS1.B (B) Modeling Conservation of Matter - FINAL (WND 1-7-2014)

Module: Modeling Conservation of Matter

DCI: PS1.B (B) The total number of each type of atom is conserved, and thus the mass does not change.

PE: MS-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.

 [Clarification Statement: Emphasis is on 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.]

This is simply a conservation of mass standard.  We won't be doing anything with identifying whether or not a chemical reaction has taken place.  Instead, we can just look at the number and type of atom in chemical reactions and get at the fact that the number must be conserved. It's probably outside of the standard to do any kind of naming of subscripts or coefficients (though it is implied by the fact that students must be able to count atoms). 

Possible Question Starters: 

"A student is using beads to model the chemical equation provided, using the following key. 

Element	Color of Bead
Magnesium (Mg)	Black
Chlorine (Cl)	Blue
Sodium (Na)	White
Flourine (F)	Green

MgCl₂ + 2NaF → MgF₂ + 2NaCl

In order to correctly model all of the  chlorine atoms involved in this equation, how many blue beads should the student use? 

correct answer - 2

incorrect answer - 4, 1, 3

"Which of the following  provides the best evidence that the number of atoms does not change when a chemical reaction takes place? 

correct answer - The mass of a sealed plastic bag containing unreacted baking soda and vinegar equals the mass of the same sealed plastic bag after the baking soda and vinegar are mixed. 

incorrect answer - Equal masses of baking soda and vinegar were combined in a sealed plastic bag.  After the baking soda and vinegar mixed, the mass of the plastic bag had increased.