Stoichiometry of S'mores Synthesis: Lab Report

Introduction

In this experiment, the principles of stoichiometry are explored by creating S'mores, the delicious combination of chocolate, marshmallow, and graham crackers. The term 'stoichiometry' originates from 'stoichio' meaning element and 'metry' meaning the process of measuring. It involves determining the mass and quantity relationships among reactants and products in a chemical reaction.

Purpose

The purpose of this experiment is to identify the limiting reactant in the synthesis of S'mores.

Prelab Questions

1. 1. What does a chemical equation tell us?

A chemical equation represents the reactants on the left and the products on the right, indicating the compounds involved in a reaction.

1. 1. What do the coefficients in a balanced chemical equation represent?

Coefficients in a balanced chemical equation specify the relative amounts of molecules or moles of each substance involved in the reaction.

Materials

• Miniature Chocolate bars
• Graham Cracker Squares
• Marshmallows
• Paper Towels
• Bunsen Burner
• Wooden skewers

Reference Data

Substance	Symbol	Unit mass	Package Mass
Graham Cracker Squares	Gr	8.50 g	408 g
Marshmallow	Mm	7.125 g	285 g
Miniature Chocolate Bar	Ch	12.00 g	348 g

Procedure

1. 1. Perform a synthesis reaction (forming one S'more):
      • Determine the formula for a S'more.

A S'more consists of 2 graham cracker squares, 1 marshmallow, and 1 miniature chocolate bar.

1. 1. • Write the balanced chemical equation.

2Gr + 1Mm + 1Ch → 1S'more

1. 1. • Complete the following ratios based on the balanced equation:

Ratio	Value
2 Gr = 1 Mm	2 Gr = 1 Mm
2 Gr = 1 S'more	2 Gr = 1 S'more
1 Ch = 1 Mm	1 Ch = 1 Mm
1 Ch = 2 Gr	1 Ch = 2 Gr
1 Ch = 1 S'more	1 Ch = 1 S'more
1 Ch = 1 Gr	1 Ch = 1 Gr

1. 2. Calculating the unit mass of the S'more:
      • Calculate the mass of ONE S'more:

Gr = 8.50 g x 2 + Mm = 7.125 g + Ch = 12.00 g = 36.12 g

1. 1. • Is there a relationship between the mass of a S'more and the masses of the reactants used to make it?

Yes, the mass of the reactants combined equals the mass of the S'more.

1. 1. • What law defines this relationship?

The Law of Conservation of Mass.

1. 2. Predicting the limiting reactant:
      • Complete the data table based on the materials provided for your group:

Substance	Quantity	# of S'mores it COULD make
Graham Cracker Squares	42	21
Marshmallow	55	55
Miniature Chocolate Bar	11	11

1. 1. • What will the limiting reactant be?

The limiting reactant will be the Miniature Chocolate Bar.

1. 1. • How many of the other substances will remain?

4 marshmallows and 2 graham cracker squares will remain.

1. 1. • What are the masses of each excess reactant that will remain once the reaction is complete?

Excess Graham Cracker Squares: 2 Gr = 17 g; Excess Marshmallows: 4 Mm = 28.5 g

1. 2. Determining the limiting reactant experimentally:
      • How many S'mores do you predict you will be able to make using your reagents?

Based on the limiting reactant (1 Miniature Chocolate Bar), we predict we can make 11 S'mores.

1. 1. • Test your hypothesis by performing the S'more synthesis reaction until one reactant is used up. Were you correct?

Yes, we were correct. The reaction stopped when the Miniature Chocolate Bar was completely used.

1. 1. • Why or why not?

Because the Miniature Chocolate Bar was the limiting reactant, and once it was depleted, the reaction could not proceed further.

Post Lab Questions

1. 1. S'more synthesis reaction:
      • If given 102 g of graham cracker squares, 85.5 g marshmallows, and 96 g chocolate, what is the limiting reactant in this S'more synthesis reaction?

The limiting reactant is graham cracker squares (Gr).

1. 1. • How many of each excess reactants will remain?

Excess Chocolate (Ch): 24 g; Excess Marshmallows (Mm): 14.25 g

1. 1. • What is the mass of each excess reactant remaining?

Mass of Excess Chocolate (Ch): 24 g; Mass of Excess Marshmallows (Mm): 14.25 g

1. 2. Marshmallow madness:
      • Using the unit mass and package mass provided, how many marshmallows are available in a whole package?

There are 40 marshmallows in a whole package.

1. 1. • Determine the units of graham crackers and chocolate segments needed to consume an entire package of marshmallows.

You would need 80 graham cracker squares and 40 miniature chocolate bars to consume an entire package of marshmallows.

1. 1. • Using the unit masses, determine the mass of graham crackers and chocolate segments needed.

The mass needed is 680 g of graham crackers and 480 g of chocolates to consume an entire package of marshmallows.

1. 1. • How many bags of marshmallows and bags of miniature chocolate bars are needed to make this many S'mores?

You would need 2 bags of marshmallows and 2 bags of miniature chocolate bars to make this many S'mores.

1. 2. Graham Cracker Insanity:
      • Using the unit mass and package mass provided, if you are given one box of graham crackers, what is the maximum number of S'mores that can be made?

The maximum number of S'mores that can be made with one box of graham crackers is 46.

1. 1. • Determine the units of marshmallows and chocolate segments needed to consume an entire package of marshmallows.

You would need 46 units of marshmallows and 23 units of chocolate to consume an entire package of marshmallows.

1. 1. • Using the unit masses, determine the mass of marshmallows and chocolate segments needed.

The mass needed is 759 g of marshmallows and 494.5 g of chocolates to consume an entire package of marshmallows.

1. 1. • How many bags of marshmallows and bags of miniature chocolate bars are needed to make this many S'mores?

You would need 1 bag of marshmallows and 2 bags of miniature chocolate bars to make this many S'mores.