Colby College
Harry Potter Potions Class: Troll Toothpaste
Teacher’s Instructions
Average length: 30-40 minutes
For grades K-5
Objectives:
• Students will determine the difference between physical and chemical changes
• Students will observe the affects of a catalyst on a reaction
• Students will observe the decomposition of hydrogen peroxide
o 2H2O2(l) → H2O(l) + 2O2(g)
Key Terms:
Catalyst: a substance that is not consumed by a chemical reaction but increases the rate at
which the reaction occurs.
Chemical Change: a change that alters the (molecular) composition of a substance.
Chemical Reaction: a process by which a substance is converted to a different substance.
Decomposition Reaction: A reaction where a single compound is broken down into
simpler compounds.
Exothermic Reaction: a chemical reaction that releases heat to its surroundings.
Physical Change: a change that alters the state or appearance of a substance but not its
chemical composition.
Materials: per student
• One plastic tub (~8 x 12 in)
• One empty 16-oz cup
• One 9-oz cup
• Two spoons
• ½ cup of 3% hydrogen peroxide solution
• Packet of active yeast (¼ ounce)
• Liquid dishwashing detergent (just a squirt)
• Food coloring
• Warm water
Safety Instructions:
• Wear safety goggles at all times to ensure that materials will not irritate eyes
• Gloves and other personal protective equipment are optional
Procedure:
1. Divide students into pairs preferably (no more than three to a group, in order to ensure that each student will be able to contribute to the experiment)
2. Outfit each student with a pair of safety goggles
3. Place the plastic tub at the center of the desk with the 16-oz cup in its center
4. Pour ½ cup of hydrogen peroxide (dragon tears) solution into the 16-oz cup
a. Add a squirt of dish soap (goblin snot) to the hydrogen peroxide
b. Add a few drops of food (beetle juice) coloring to the hydrogen peroxide and dish soap mixture
5. In a separate container, mix the packet of yeast (spider eggs) with 1/8 cup of warm water
a. Mix water and yeast together until the mixture is watery (~90 seconds)
i. Use the second spoon to remove clumping yeast from the first spoon
ii. Continue stirring the yeast/water mixture
6. Finally, pour the yeast mixture into the peroxide mixture
a. A copious amount of foam is produced
Clean-up Instructions:
• Wash hands
• All materials are safe to be poured down the drain
• Cups, spoon, measuring apparatuses, and plastic tub are reusable
How it works:
Think of hydrogen peroxide (H2O2) as water (H2O) with an extra oxygen atom attached to it. Hydrogen peroxide readily decomposes to yield two products (liquid water and oxygen gas).
2H2O2(l) → H2O(l) + 2O2(g)
Yeast contains catalase which acts as a catalyst for this reaction by causing the peroxide molecules to release its extra oxygen atom at an increased rate. The dish detergent collects the oxygen (O2(g)) that is released causing the intense foam to form.
Note that the cup feels warmer after the reaction has taken place. The heat is due to the exothermic reaction that took place during the decomposition of the hydrogen peroxide. An exothermic reaction is a chemical reaction that releases heat as the products are formed.
Due to the exothermic reaction, a more accurate depiction of this decomposition reaction is:
2H2O2(l) → H2O(l) + 2O2(g) + heat
Harry Potter Potions Class: Troll Toothpaste
Pupil’s Instructions
Ingredients:
• ½ cup of dragon tears
• A dash of goblin snot
• 5 drops of beetle juice
• 1 tbsp of spider eggs
• 1/8 cup of water from the Black Lake
Other Materials:
• Large plastic tub
• Cauldron (16-oz. cup)
• Magic mixing bowl (9-oz. cup)
• Two spoons
Procedure:
1. Adorn safety goggles
2. Place the tub at the center of the desk with the cauldron in it
3. Pour ½ cup of dragon tears into the cauldron
a. Add a dash of goblin snot to the dragon tears
b. Add five drops of beetle juice to the dragon tears and goblin snot
4. In the magic mixing bowl, mix the spider eggs with 1/8 cup of warm Black Lake water
a. Mix Black Lake water and spider eggs together until the mixture is watery (~1.5 minutes)
5. Finally, pour the egg mixture into the dragon tears mixture
[pic]
Harry Potter Potions Class: Troll Toothpaste
Pupil’s Worksheet
[pic]
1. What did you observe during the reaction?
Draw the final product (the troll toothpaste):
[pic]
2. Was this a chemical or physical reaction?
3. Which ingredient caused the reaction to speed up? (Which step in our recipe caused the reaction to happen quickly?)
4. Which is a physical change? (circle your answer)
a) melting ice into liquid water
b) burning wood
c) mixing baking soda (base) and vinegar (acid)
5. Which is a chemical change? (circle your answer)
a) putting food coloring in water
b) water becoming ice
c) rust forming on a nail
References:
Tro, Nivaldo J. Chemistry: A Molecular Approach. Upper Saddle River: Pearson Education, Inc.
2008. Print.
Kid-Friendly Elephant Toothpaste Demo. Guide. Web. 7 Jan. 2010.
.
"Reeko’s Mad Scientist Lab: Elephant Toothpaste." Reeko’s Mad Scientist Lab: Elephant . Web.
9 Jan. 2010. .
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