LAB: S'mores and the Mathematics of Chemical Reactions



Name: _____________________________ Hour: _____

LAB: S’mores and the Mathematics of Chemical Reactions

CAUTION: Do not let any of your food stuffs touch the lab bench and do not use any lab equipment to handle the food. DO NOT EAT ANY OF THE FOOD UNTIL INSTRUCTED TO DO SO.

Introduction: Almost everyone knows what S’mores are. They are cookies made from two graham crackers, three pieces of Hershey's chocolate, and one marshmallow. We’ll be making “mini S’mores” with Golden Grahams, mini marshmallows, and chocolate chips. This recipe is much like a chemical equation. In fact, it can be written as the following chemical equation:

2Gg + 3Cc + Mm ( Gg2Cc3Mm

where:

Gg = a Golden graham cracker ‘atom’

Cc = a chocolate chip ‘atom’

Mm = a marshmallow ‘atom’

Gg2Cc3Mm = the 'chemical formula' of a S’more cookie 'molecule'

The equation above states in symbolic terms how to make a S’more cookie. Just like a chemical equation, it also tells us how much of each component to use.

1. Suppose you were given 4Gg, 6Cc, and 2Mm. How many Gg2Cc3Mm could you make?

2. Suppose you were given 6Gg, 9Cc, and 3Mm. How many Gg2Cc3Mm could you make?

These questions are easy since each component is a multiple of the basic S’mores recipe, but what if you were given ingredients which are not multiples of the basic recipe?

3. Open your S’mores kit and count how many of each ingredient you have (don’t count partial pieces):

# of Gg _____ # of Cc _____ # of Mm ______

4. How many complete S’mores could you make?

This is not too difficult either, since the number of each component are easy to manage. Notice that some of the ingredients are leftovers. Chemical reactions are like this too. Sometimes chemists mix compounds and the resulting reaction does not consume all of the reactants. The leftover reactant is said to be in excess. The reactant which is completely consumed is called the limiting reactant, because it is the reactant which limits the amount of product formed in the reaction.

5. For example, say you have 12Gg, 15Cc, and 9Mm:

a. How many S’mores could you make? ____________

b. What component was the limiting reactant? ___________________

c. Which components were in excess? _________________________________________

6. Using your own S’more data, which component was the limiting reactant? __________________

7. Using your own S’more data, which components were in excess? ________________________

8. Now suppose you have a bag containing 64 'atoms' of Gg and an excess of Mm and Cc. Calculate how many S’mores can be made from the ingredients. Explain your reasoning and show your work. When you have finished this question, have your teacher check and initial your lab report.

2Gg + 3Cc + Mm → Gg2Cc3Mm

Teacher Initials: __________

Use the mass information supplied below to answer the questions that follow.

1 Gg 'atom'= 0.357 grams

1 Cc 'atom' = 0.510 grams

1 Mm 'atom' = 0.616 grams

9. Now suppose you have a sealed bag containing an unknown number of Gg, Mm, and Cc. Instead of knowing the number of each, you are given the mass of an ingredient. Suppose you know that the bag contains 54.97 grams of Gg and an excess of Mm and Cc.

a. What is the mass of a single Gg 'atom'?

b. How many 'atoms' of Gg are in the bag? Show your work.

c. How many 'molecules' of Gg2Cc3Mm (the number of S’mores) could you make from these ingredients? Show your work.

2Gg + 3Cc + Mm → Gg2Cc3Mm

d. What is the mass of one S’more? This is also known as the molar mass. Show your work.

e. What is the total mass of all of the S’mores that you could make from these ingredients? Show your work.

Teacher Initials: __________

When the answers to the previous questions have been checked, you can make S’mores and enjoy them while you try to figure how to complete the additional questions below.

In trying to draw an analogy between the 'chemical reaction' for a S’more cookie and a real chemical reaction, you might consider the given masses as the 'atomic mass' of atoms of Golden graham cracker atoms, chocolate chip atoms, and marshmallow atoms. The whole numbers in front of each component of a reaction can stand for an individual chemical unit as well as for a dozen, a mole, or any other counting unit.

1. Assume you have excess Gg but only 9 Cc. How many Mm would be required to completely react with the 9 Cc? Show your work.

2Gg + 3Cc + Mm → Gg2Cc3Mm

2. Assume you have excess Mm but only 24 Gg. How many Cc would be required to completely react with the 24 Gg? Show your work.

2Gg + 3Cc + Mm → Gg2Cc3Mm

3. Assume you have excess Gg but only 4.5 Cc. How many Mm would be required to react completely with 4.5 of Cc? Show your work.

2Gg + 3Cc + Mm → Gg2Cc3Mm

4. Assume you have 178.5 grams of Gg:

2Gg + 3Cc + Mm → Gg2Cc3Mm

a. How many Gg are there in 178.5 grams of Gg? Show your work.

b. How many Cc would be required to react completely with the 178.5 grams of Gg? Show your work.

c. How many grams of Cc would be required to react completely with the 178.5 grams of Gg? Show your work.

5. How many grams of S’mores would be produced from the complete reaction of 193 grams of Cc?

2Gg + 3Cc + Mm → Gg2Cc3Mm

a. First, determine how many Cc are equivalent to 193 grams. Show your work.

b. Now determine how many S’mores you can make. Show your work.

c. Finally, determine the mass of that number of S’mores. Show your work.

Apply the methods you have learned to solve the following simple chemical reactions.

6. How many aluminum sulfide are produced from 6 aluminum reacting with an excess of sulfur? Show your work. Hint: solve this problem just like you did problem #3 on the previous page.

2Al (s) + 3S (s) → Al2S3 (s)

7. How many grams of aluminum sulfide are produced from 96.18 grams of sulfur reacting with an excess of aluminum? Show your work. Hint: solve this problem just like you did problem #4 on the previous page.

2Al (s) + 3S (s) → Al2S3 (s)

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