Chemistry

Standard 4, Objective 2

Title: S’mores lab

Description: Students will relate the making of s’mores to limiting reagents and theoretical and actual yields

Time needed: 30-40 min; 10 minutes to give instructions and 20-30 minutes for the students to make their s’more and respond to the questions.

Prior Knowledge: Students should have a basic knowledge of balancing equations, limiting reagents, theoretical, actual and percent yields.

Materials Needed: Each student will need: 1 whole graham cracker, 1 marshmallow, 1 fun size Hershey bar. I have about 120 students and I bought 3 boxes of graham crackers, and 2 bags of jumbo marshmallows and a fun size candy bar for each student. You can buy the large Hershey bars and just break off the needed number of squares.

Safety Considerations: None

Procedure:

  1. Pass out the student sheet to each student and read the instructions aloud as they follow along. (The more dramatic the better) Explain that for the students to obtain the necessary materials to perform the lab they must first pass off their pre-lab questions.
  2. Once their pre-lab questions are completed students can then assemble their s’mores and eat them while they respond to the questions. I use this activity to help students conceptualize the vocabulary without being overwhelmed with too much math. Students seem to grasp the concept better and then we can move on to the math steps.

Scoring: I gave students 10 points for participating and an additional 10 points for completing the student sheet correctly.

Student SheetName______Period___

Title: S’mores Lab

Introduction: It is obvious to the most casual observer, that the making of the epicurean delight known as the s’more is not child’s play. In fact, it is a study of quantitative relationships involving stoichiometry and should only be undertaken by persons with sufficient training, such high school chemistry students.

Pre-lab Questions:

  1. What are the main parts of a written chemical equation?
  1. What does the term limiting reagent mean?
  1. How is theoretical different from actual yield?
  1. How do you think they are both helpful in working with chemical reactions?
  1. What is percent yield? (include the equation)

Advanced Lab Procedures:

1. The balanced equation for the reaction we are about to study is:

2Gch + 1M + 6Sq → 1S’mo

When: Gch = Graham Cracker Half

M = Marshmallow

Sq = Squares of Chocolate

S’mo = S’more

2. Using your balanced equation, combine your reactants to get the desired product and then ENJOY!

Data: (draw or describe the reactants and products)

Analysis:

  1. Given 18 squares of Chocolate, how many S’mores can you make if the other ingredients are in excess?
  1. If you wished to make 3.5 S’mores, how many Graham Cracker Halves would be needed?
  1. Given 7 Graham cracker halves, 2 marshmallows and 20 squares of chocolate:

(a) What is the limiting ingredient?

(b) What is the theoretical yield of S’mores?

  1. While doing the experiment described in question 3 above some sugar-starved low life steals some of your ingredients and you are only able to make 2 S’mores. What is your percent yield?