Summary

In this demonstration, students will learn about chemical reactions by observing the differences when 4 small cakes are baked. Each recipe will differ slightly in that one important ingredient will be left out in 3 of the 4 mixtures. Students will observe and discuss what happens when things are missing or left out of a mixture and how that effects the chemical reaction.

Grade Level

Elementary School

Objectives

By the end of this demonstration, students should be able to:

• Determine, though observation, that a chemical reaction has taken place.
• Record observations of physical and chemical changes.
• Understand the meaning of chemical reaction.

Chemistry Topics

This demonstration supports students’ understanding of

• Chemical reactions
• Chemical Change
• Physical Change
• Observations

Time

Teacher Preparation: 30-45 minutes

Lesson: 45-60 minutes

Materials

• Mixing bowl
• Measuring spoons
• Whisk
• Gloves for handling cooked food
• Knife for cutting cakes
• 4 Mini loaf pans
• Non-stick spray
• Ingredients are for 1 cake (you will need 4):
  
  • 6 tablespoons flour
  • 3 tablespoons sugar
  • Pinch of salt
  • 3 pinches baking powder
  • 2 tablespoons milk
  • 2 tablespoons cooking oil
  • ¼ teaspoon vanilla
  • 1 egg* (beat egg in cup/bowl: use only 1/3 of it in each cake.)

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• Exercise caution when using a heat source.
• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
• Food in the lab should be considered a chemical not for consumption.

Teacher Notes

• I recommend this demonstration for 3^rd grade students or higher.
• As mentioned above, you will be making 4 separate cakes. In the essence of time or if you do not have an oven available to you at school, you can make and bake the 4 cakes at home, and then mix 4 more in class for demonstration and through the “Magic of TV” pull out the already baked cakes.
• If you don’t have mini loaf pans, make your own pans by covering the outside of a cereal bowl with several layers of aluminum foil to form a mold. If you create molds, you will need a cake pan or other container to support the mold.
• Baking instructions:
  • Preheat oven to 350 degrees.
  • Cake #1:
    • Oil the inside of your cake pan with non-stick spray.
    • Mix all of the dry ingredients together.
    • Add the wet ingredients, only using 1/3 of the egg.
    • Stir until smooth and all the same color.
    • Pour batter into the pan.
    • Bake for 15 minutes
      
  • Cake #2-4 - Repeat above steps:
    • Leave the oil out of one recipe
    • Leave the baking powder of one recipe.
    • Leave the egg out of one recipe.

• Assist students in filling out table with the missing items in their observation table.
• Observation: Cut all 4 cakes in half and look at the insides. Pass cakes around so students can get a close look.
• Do they look different?
• Optional: This is an exception to the “Do not eat or taste your science experiments!” If you are going to let students taste the cake, you do not want students handling the food during the above observation. You may want to just walk around with the cakes and allow them to observe, or have another batch for tasting.
• Teacher discretion required: Cut the cake in to small pieces, enough to go around. Have students taste the cake. Do they taste different?
• What happened?
  • Heat helps some chemical reactions to occur as the cake bakes.
  • Heat helps baking powder produce tiny bubbles of gas, making the cake light and fluffy (this is called leavening.)
  • Heat causes protein from the egg to change and make the cake firm.
  • Oil keeps the heat from drying out the cake.