Name: ______________________ Date: _______________ Block: ___
Partners: _________________________________________________
Introduction: You have spent a lot of time studying the various types of reactions that can occur in
chemistry. You have also become experts in balancing chemical equations.
In this activity, you will be introduced to simple stoichiometry. Stoichiometry is the chemical term to
describe calculations that allow us to find the amounts of chemicals involved in a given reaction. When
you hear stoichiometry, think quantitative relationships.
In stoichiometry, you must always start with a balanced equation! We will use the following recipe
(equation):
2 Gc + 1 M + 1 Cp  1 S’more
where the elements are:
Gc = graham cracker, Cp = chocolate piece, M = marshmallow
1. Notice that to make this recipe you have 4 pieces (reactants) to the left of the arrow and 1 piece
(product) to the right. This is supposed to represent a balanced equation, so how can 4 = 1? Explain.
2. What type of chemical reaction does this represent? ___________________
3. Write out the actual “formula” for a S’more using subscripts and the parts (elements) from which it
is made. Remember the Law of Conservation of Mass. You must account for all the reactants in your
product. _______________________
4. Now rewrite the balanced chemical equation you see above, but in place of the “S’more”, write in its
actual formula. Illustrate the reaction.
5. If each student is to make one S’more, and I have 20 students, how much of each ingredient will I
need? Explain your logic using the chemical equation above.
Gc:
Cp:
M:
For questions 6 – 7a & b, Use DIMENSIONAL ANALYSIS
6. If I have 20 graham crackers, how many marshmallows and chocolate pieces will I need to make
S’mores? How many S’mores can I make?
_______________________
7. a. Mrs. McCord asks Mr. McCord if he minds if she uses a chunk of their November grocery budget
to buy ingredients for S’mores for all 90 of her students so they can have some fun learning
stoichiometry. He asks, “Well, it depends, how much of each ingredient do you need to make 1 S’more
per student?” Answer his questions using Dimensional Analysis.
_______________________
b. Mr. McCord said, “Well, I guess they’re lucky that I love you so much, so ‘Yes.’ “ While gathering
the ingredients at Publix for 90 students, I could only purchase 30 graham crackers because there
had been a sale on graham crackers, and there was only one box left! How does this affect the
number of S’mores that can be made?
_______________________
c. How many more graham crackers does Mrs. McCord need to buy make S’mores for all 90
students?
_______________________
You are now ready to bring this sheet
to Mrs. McCord for checking!
After your paper is checked, obtain reactants from Mrs. McCord.
Safety: Do not eat until instructed. Follow standard safety protocol around the Bunsen burner.
Reactants:
Apparatus:
(fill in blank with quantity given to your group)
___ graham crackers
___ marshmallows
___ pieces of chocolate
goggles
bamboo skewer stick
matches
Bunsen burner
aluminum foil
A reactant that is left over is said to be in excess and those that are used up limit the
amount of product that can be made and are thus called limiting reactants.
8.
How many S’mores can you make from these combinations?
2 Gc +
1 M + 1 Cp
 ___ S’more
4 Gc + 2 M + 2 Cp  ___ S’more
10 Gc + 5 M + 5 Cp  ___ S’more
9. Continue to figure the possible number of S’mores. Use the spaces to the left of the equation to tell
how much of each ingredient will be left over.
____________________
2 Gc + 1 M + 2 Cp  ___ S’more
____________________
3 Gc + 1 M + 1 Cp  ___ S’more
____________________
5 Gc + 1 M + 3 Cp  ___ S’more
For questions 10 - ______, Read each reaction. Using your reactants from Mrs. McCord, put the
reactants into as many products as possible.
10. Reaction #1: One chocolate piece reacts with one graham cracker to produce one chococracker.
a. Write the reaction sentence in the form of a chemical equation.
Remember to use Gc = graham cracker, Cp = chocolate piece, M = marshmallow
b. Draw a box around each coefficient.
c. Illustrate each reaction.
d. What is the excess reactant? ____________________________
e. What is the limiting reactant? ____________________________
f. How much of the excess reactant is leftover? _________________
11. Reaction #2: One marshmallow reacts with four graham crackers to form a gramallow.
a. Write the reaction sentence in the form of a chemical equation.
b. Draw a box around each coefficient.
c. Illustrate each reaction.
d. What is the excess reactant? ____________________________
e. What is the limiting reactant? ____________________________
f. How much of the excess reactant is leftover? ________________
12. Reaction #3: Two chocolates react with two marshmallows to form a chomallow.
a. Write the reaction sentence in the form of a chemical equation.
b.
c.
d.
e.
f.
Draw a box around each coefficient.
Illustrate each reaction.
What is the excess reactant? ____________________________
What is the limiting reactant? ____________________________
How much of the excess reactant is leftover? ________________
13. Reaction #4: One Graham Cracker reacts with three chocolates to form a gracolate.
a. Write the reaction sentence in the form of a chemical equation.
b. Draw a box around each coefficient.
c. Illustrate each reaction.
d. What is the excess reactant? ____________________________
e. What is the limiting reactant? ____________________________
f. How much of the excess reactant is leftover? ________________
You are ready to bring this second sheet to Mrs. McCord for checking!
After it is checked, obtain bamboo skewer and matches from Mrs. McCord.
Step 1) Go to a Bunsen burner and light it.
Step 2) Put your Cp onto 1 of your Gc.
Step 3) Roast your M over the Bunsen burner until golden brown!
Step 4) Quickly place the M onto the Cp and cover with your other Gc. Wait for loss of heat energy.
Step 5) Eat the product and create a chemical decomposition reaction in your mouth!
Conclusions, Error Analysis, and Comments
Name: ______________________ Date: _______________ Block: ___
Partners: __________________________________________________
Conclusions
1. Given the amount of ingredients listed below, circle the limiting ingredient (i.e. the one that runs
out first); then put a box around the excess ingredients (the ones you have extra of).
a. 2 graham crackers + 2 marshmallows + 2 chocolate pieces
b. 6 graham crackers + 4 marshmallows + 2 chocolate pieces
c. 6 graham crackers + 5 marshmallows + 8 chocolate pieces
2. If you had one full box of graham crackers, a full bag of marshmallows, and a full chocolate bar,
what would the limiting reactant be? Explain your answer.
3. How many S’mores would you be able to make with the amounts of ingredients listed in question
2? (You will need to do some research on your own.)
4. Define “limiting reactant” and “excess reactant” in your own words based on your observations in
this activity.
5. Now tie the idea to chemistry. The synthesis reaction between hydrogen and oxygen shown below
is a little bit like “synthesizing” S’mores from graham crackers, chocolate pieces and
marshmallows.
2H2 + O2  2H2O
a. What is the ratio of hydrogen to oxygen needed to produce 2 moles of water in this
reaction?
b. The chart below shows three experiments, each with different amounts of reactants.
Circle the limiting reactant in each experiment. (HINT: this can be determined with math
or by drawing pictures like you did with the S’more Stoich’ Lab.) Then determine the
number of moles of water that will be produced when the limiting reactant is used up.
Starting amount
of H2
Starting amount
of O2
Experiment 1
8 moles
12 moles
Experiment 2
6 moles
6 moles
Experiment 3
12 moles
8 moles
Experiment 4
12 moles
2 moles
Experiment 5
6 moles
4 moles
Amount of water
predicted
Complete the following to finish your lab report…
Error Analysis: (at least 2 sentences)
Comments: (at least 2 sentences)