Summary

In this lab, students will be able to demonstrate the difference between a physical and chemical change by making ooey, gooey, yet yummy S’mores!

Grade Level

Middle School

Objectives

By the end of this lab, students should be able to

• Identify a physical change (breaking apart the cracker with their hands, chewing the cracker with their teeth, and melting the chocolate with the heat).
• Identify a chemical change (breaking the cracker down with salivary amylase, using the heat to break down the sugar molecules within the marshmallow).
• Apply the Scientific Method to a laboratory experience.

Chemistry Topics

This lab supports students’ understanding of

• Physical change
• Chemical change
• Chemical Reactions

Time

Teacher Preparation: 5-10 minutes

Lesson: 30 minutes

Materials

• 1 marshmallow per student
• 1 whole graham cracker per student
• 1 kabob stick per student (may be cut in half due to their length)
• 1 miniature chocolate bar (they just need 1 small square of chocolate)
• A Bunsen burner (or alternative heat source to roast the marshmallow)
• Flint (something to light the burner with)
• 1 paper towel per student
• Student handout
• Pencil

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Always use caution around open flames. Keep flames away from flammable substances.
• Always be aware of an open flame. Do not reach over it, tie back hair, and secure loose clothing.
• Open flames can cause burns.
• When lighting the burner, be cautious with the flame.
• An operational fire extinguisher should be in the classroom.
• Food in the lab should be considered a chemical not for consumption. (This is to your discretion as I allowed my kids to eat their finished product.)

Teacher Notes

• Demonstrate what the students will do first. Start with how to correctly line-up to obtain their material all the way to discarding their trash.
• Have each material already grouped either at each table or have a “buffet” style set-up on the counter for each student to quickly grab 1 and go. I would also recommend manning that station.
• Have the students develop their own hypothesis as well as write down any “before” observation for the cracker, marshmallow, and chocolate. In addition, have them write down the materials after they collect them. This keeps the sitting ones busy while the others are gathering materials.
• Background: physical changes are reactions that although physically change the object, it does not change what the substance is made of. In a chemical reaction either a new substance is formed or energy is given off or absorbed
• Differentiation: For the “lows” simply have them focus more on the before and after part of the results section vs focusing on giving a proper scientific method. The middles, keep experiment as is. For the “highs” have the students explain how the Digestive System further aids in the chemical reaction part; focusing more so on how Macromolecules within the marshmallow are broken down into their simpler parts. You can also have them identify the macromolecule as well as have them determine its simpler form.
• *Extension: When all of these food items enter our stomachs filled with digestive juices (such as acids) what do you think will happen to the food? Will it undergo more changes? If so, will they be physical or chemical?
• *Options: you could also have the students collect the mass of the material throughout the experiment to demonstrate conservation of mass
• Conclusion: The difference between a physical change and chemical change is: a physical change does not change the structure of atoms or molecules but it does change the overall structure of the ingredient. For example the cracker being broken down from a whole into 2 pieces. On the contrary, a chemical change will rearrange the bonds between atoms and produce new substances with new properties. As we demonstrated by breaking the cracker, melting the chocolate, and chewing the ingredients, physical changes took place as the contents were still the same just physically different. We also demonstrated chemical changes by burning the marshmallow and by allowing the enzymes within our saliva break down the food even further. From that point, the ingredients were changed and were no longer the same chemically.