Teacher S Instructions

Elephant Toothpaste

Teacher’s Instructions

Teaching objectives:

Students will observe several examples of chemical and physical reactions
Students will carry out the decomposition reaction of hydrogen peroxide
Students will describe and illustrate the changes of the hydrogen peroxide chemical reaction

Recommended Grades: K-5

Estimated Time: about an hour

Key concepts and terms:

Reaction: a transformation or change

Chemical Reaction:a process in which one substance is converted into a new substance with new properties

Physical Reaction: a process in which a substance changes in size, shape or color but does not change in composition.

Catalyst: A substance that alters the speed of a chemical reaction

Procedure:

Over all tables, drape trash can bags to try and prevent excess mess. At each student’s seat, place a cake pan or plastic bin, an empty soda bottle with its cap, a closed container with ½ cup hydrogen peroxide, a container with 1 tsp dry active yeast, and a spoon. At each table set out a container of food coloring.
Ask the class to give examples of reactions. Tell them baking a cake is a kind of reaction, and so is blowing out a candle. Give examples of both a chemical and a physical reaction. If you want, play the Chemical vs. Physical Game (See Supplementary Exercises).
Tell the class that they will be working with a chemical called Hydrogen Peroxide, or H2O2. This is a fairly non-toxic chemical, but they should be wearing goggles. Show them a picture of the molecule, and how it breaks down with very slowly into water and oxygen.
Ask the class what would happen if the hydrogen peroxide turned into water and oxygen VERY fast. Tell them that a reaction helper called a catalyst can help a reaction speed up.
If there is room in the class, hand out the worksheet.
Tell everyone to carefully open the hydrogen peroxide container. Using a funnel, have the students carefully pour the liquid into the bottles. After pouring, tell the students to put caps back on their bottles.

Tell students they can choose a color food dye to put in their bottles. Let them carefully squeeze 4-5 drops into the bottle if they want to. Help them add one squirt of Dawn dish detergent, and then have them put the caps back on their bottles.
Heat up the water. Plan on bringing extra, because some may evaporate. The water doesn’t have to boil, but it should be just warm enough to dissolve yeast (and not hot enough to burn anyone!)
Distribute ~10 mls (2 tsp) of water to each student in their yeast container. Tell them to stir the yeast with the spoons until it looks smooth and not lumpy. If students need something to do, have them gently swirl their bottle. Tell them not to shake it (the reaction won’t work well if they do). Wait until everyone is ready.
Explain to the class what everyone is going to do. Tell them not to do anything until you say ‘Go!’. Tell the students they will uncap their bottles, pour the brown solution (the helper or catalyst) into their bottles, and wait. Tell them they can touch the bottle and articulate their observations (the reaction is exothermic, so the bottle should feel warm.) If there is a sink and plenty of paper towels in the room, tell them they can touch the foam gently. Ask everyone if they understand what they are going to do. If you feel confident they are ready and you are ready, say “Ready? Go!”
Ask students to talk about what they see as it’s happening. What does the foam feel like? Is there anything left in the bottle?
Get students to participate in clean up activities, then have an assistant continue to clean up while you move students to new tables or to a sit-down area on the floor.
Time permitting, have students draw a sketch of the “Elephant Toothpaste.” Ask them what they thought happened. Do they think it was a chemical or a physical reaction? Hand out the Elephant Toothpaste recipes so they can try the experiment at home with their families.

Why it works:

Hydrogen peroxide is an oxidizing agent. Over time, it is converted to water and oxygen in a decomposition reaction according to the following formula:

2 H2O2 --> 2 H2O + O2

However, this reaction goes very slowly. It is, however, favorable, and is

exothermic: it releases some heat as it takes place. Reactions can speed up by

adding heat, adding more reaction materials, or adding a catalyst. In the case of

the Elephant’s Toothpaste, the yeast is a catalyst which makes the hydrogen

peroxide release the oxygen faster. The reaction is exothermic, meaning that heat is released as the reaction proceeds. The detergent is added as a surfactant: it allows the catalytic yeast to react with as much of the hydrogen peroxide as

possible.

Supplementary exercises

Chemical vs. Physical Game: Make up some cards ahead of time that depict chemical or physical changes. Show each card to the class and ask them to guess if the change is chemical or physical.

Physical reaction: Bring in some snow from outside, or ice from a freezer. How did the water change? What color is snow? What color is water? Freezing and melting are examples of physical reactions.

Chemical reaction: Take an empty bottle and add vinegar to it (about a cup). Wrap about 2 tbsp. of baking soda loosely in aluminum foil, stick it in the bottle, and put the cork in. Keep the bottle pointing upward, and shake vigorously. Kapow! This is an example of a chemical reaction.

REFERENCES:

1. Elephant’s Toothpaste – Kid Friendly. Online: <

Elephant Toothpaste

Materials List

20-30 empty plastic soda bottles, 24 oz. or smaller, with caps

3% Hydrogen peroxide: 120 mls (about ½ cup) per child

Dawn ultra concentrated dishwashing detergent (works the best, though others can be substituted)

Sealable containers to hold hydrogen peroxide

Containers to hold yeast mixture

Yeast: 1 tsp per child

Water: 2 tsp per child

Plastic spoons

Plastic funnels

Heating device for water (microwave, hot plate, electric kettle)

20-30 Cake pans or large plastic bins

Food coloring

Glitter

Garbage bags

Goggles for children

Age-appropriate worksheets (below)

Elephant Toothpaste

Recipe

You can make elephant toothpaste at home!

You will need:

3% Hydrogen Peroxide
An empty soda bottle with a cap (16 oz. or smaller)
Dawn dishwashing detergent
A large cake pan
Yeast
Warm water (not boiling)
Food coloring
Smock or lab coat
Goggles
An adult
A place it’s okay to make a mess!

Procedure

First, put on your smock or lab coat and goggles. Always be careful when doing chemistry, even in the kitchen.
Set the empty soda bottle inside the cake pan.
Have an adult help you get ½ cup of the hydrogen peroxide and pour it into the empty soda bottle.
Add 4-5 drops of food coloring and one squirt of the dishwashing detergent. Cap the bottle tightly.
Don’t shake the bottle, but swirl it around gently so that the ingredients can mix.
Mix 1 tsp of yeast with 2 tsp hot water until it dissolves and there are no more lumps.
Uncap the soda bottle and quickly pour in the yeast mixture. Yikes! The bottle will be warm from the reaction, and the foam is safe to touch (it’s just oxygen bubbles and soap).
Clean up! Make sure you wash your hands well before your next activity.

Name______

Date______

What did you observe when the reaction happened?

…………………………………………………………………………………………………………..

Draw a picture below of what you saw in your bottle:

Elephant Toothpaste

Recipe

Thrill your friends…scare your siblings…try making elephant toothpaste at home!

You will need:

3% Hydrogen Peroxide
An empty soda bottle with a cap (16 oz. or smaller)
Dawn dishwashing detergent
A large cake pan
Yeast
Warm water (not boiling)
Food coloring
Smock or lab coat
Goggles
A place it’s okay to make a mess

Procedure

First, put on your smock or lab coat and goggles. Always be careful when doing chemistry.
Set the empty soda bottle inside the cake pan.
Get ½ cup of the hydrogen peroxide and pour it into the empty soda bottle. This is toxic stuff, so don’t fool around with it too much.
Add 4-5 drops of food coloring and one squirt of the dishwashing detergent. Cap the bottle tightly.
Don’t shake the bottle, but swirl it around gently so that the ingredients can mix.
Mix 1 tsp of yeast with 2 tsp hot water until it dissolves and there are no more lumps.
Uncap the soda bottle and quickly pour in the yeast mixture. The bottle will be warm from the reaction, and the foam is safe to touch (it’s just oxygen bubbles and soap).

Name______

Date______

Elephant Toothpaste

What did you observe when the reaction happened?

…………………………………………………………………………………………………………..

Which ingredient caused the decomposition of H2O2 to go faster?

…………………………………………………………………………………………………………..

How else could you make your reaction go faster?

…………………………………………………………………………………………………………..

Was this a chemical or physical reaction? (circle one)

CHEMICALPHYSICAL

Name______

Date______

Elephant Toothpaste: Worksheet 1

There’s a lot of chemistry vocabulary we’ll be going over today. Fill out this worksheet and bring it to Katy or Liz at the end. If everything’s correct, they’ll have a small prize for you. Good Luck!

1. A chemical reaction is….

………………………………………………………………………………………………

2. Draw or describe an example of a chemical reaction below:

3. A physical reaction is….

………………………………………………………………………………………………

4. Draw or describe an example of a physical reaction:

5. True or False:

____ Acids react with bases

____Vinegar is a base

____ Alka-seltzer reacts with acetic acid

____An acid-base reaction is a chemical reaction

6. Which one of these clues could prove a scientific experiment involves a chemical reaction? (circle at least one)

Bill Nye does the experimentYou see a color change

You smell a gas that is released Your teacher tells you it’s a chemical reaction

7. How could you speed up a reaction? List just one way.

………………………………………………………………………………………………

8. What catalyst did we use in the Elephant Toothpaste demonstration?

………………………………………………………………………………………………

9. (Extra Credit) Why is chemistry so awesome?

………………………………………………………………………………………………

Katy Harmon

January 2008