Chemistry 112: Lesson Plan
Catherine Barry
THE STOICHIOMETRY OF S’MORES
Outcomes:
Students should be able to:
... identify and demonstrate the Law of Conservation of Matter
... write and balance a chemical equation for a synthesis reaction
... define and identify a limiting and excess reactants of a reaction
... solve stoichiometric problems relating mass to moles and mass to mass
1. Get students into groups of 4:
2. Per group: 1 paper plate with 1 chocolate bar, 6 marshmellows and 9 graham crackers.
3. “Today, we are going to learn about the Stoichiometry of S’mores. We are going to be
introduced to the basic concepts of stoichiometry and limiting reactants, as well as be
doing a little refresher on the Law of Conservation of Matter.”
4. Definitions: Stoichiometry is the calculation that allows us to determine the amount of
substance that is consumed or produced by a reaction.
Limiting reagent: the substance responsible for the reaction reaching completion. If
there was no limiting reactant, (if both reactants are added infinitely to a reaction),
would the reaction ever end? Nooo
Limiting reagentt is the reactant that there is less of. Not necessarily in mass.
5. In this laboratory experiment, we are going to be exploring the principles of
stoichiometry by building S’mores, the delicious, chocolate, marshmallow, and graham
cracker treat.
6. State the purpose of this experiment: to determine the limiting reagent in the synthesis
of S’mores.
7. Write this on the board. Allow students to come up with the symbols for each reactant
or use the following symbols.
C= chocolate piece
M= marshmallow
G= graham cracker
8. “Each of these represents an element in the periodic table. Graham cracker’s come in
twos. What else comes in twos? GENS So we are going to call graham crackers G2, a
diatomic element. “
9. Mass and record one of each reactant:
Chocolate square: _______g
Marshmallow: __________g
Graham cracker: ____________g
10. Producing one s’more, using one chocolate piece, a marshmallow and 2 graham
crackers: what type of reaction would this be?
11. Let’s write the synthesis reaction using our symbols for our reactants.
M + C + G2 -> MCG2
12. Now, in our groups, cause the reaction to go to completion by forming as many of the
products as you possibly can. Mass and record the product (one s’more).
S’more: ______g
Discussion Questions:
1. Is there a relationship between the mass of a S’more and the masses of the reactants
used to make it? If so, what is the relationship? What law is this?
2. A limiting reactant is the material responsible for a reaction reaching completion. In the
reaction, what was the limiting reactant?
3. What reactants, if any, were in excess?
4. If we had ONLY the mass of the amount of chocolate squares we had, could we solve for
how many S’mores we could produce with a balanced equation? Is this the same for the
mass of marshmallow? For graham cracker? For S’more?
5. So if we had 100g of chocolate square, we could figure out how many S’more we could
make...
Assessment: Teacher should assess as she questions throughout the experiment and during the
discussion questions. She should also watch for participation as this activity allows for
participation from everyone. (no written component)
Modifications: Each group should have a 1:1 ratio of higher level and lower level students.