Elephant Toothpaste

Age

Middle School, High School

Format

Stage Show

Materials

   100 mL or 1 L graduated cylinder
   Dish soap
   30% Hydrogen peroxide (H2­O2)
   Food coloring
   50 mL centrifuge tube
   Saturated potassium iodide (KI) solution (100 g KI to 70 mL water)
   Garbage bags or tarp
   Small fish tank 

Safety Precautions

Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience.

Hydrogen peroxide is a strong oxidizer, do not allow it to touch your skin. Do not allow any KI to get onto your skin. It will stain your clothes permanently. Wear gloves, goggles, and perhaps a labcoat. When performing the exothermic reaction ensure that observers are about four feet away. DO NOT allow children to touch the “toothpaste.”

30% Hydrogen Peroxide MSDS

Potassium Iodide MSDS

Preparation

Ensure prior to your show that you have enough saturated KI solution and hydrogen peroxide. Immediately before your show, lay out garbage bags (or tarp) under your experiment area. Half fill small fish tank with water, so you can clean out the graduated cylinder between presentations.

Demonstration

Pour about 20 mL (1/5 of the total volume of the cylinder) of hydrogen peroxide into the cylinder. Pour about 5 mL of soap into the 100 mL graduated cylinder. Then add 4 drops of food coloring. Measure out about 5 mL of KI solution. Ensure that people are standing a safe distance away. Then, add the KI to the graduated cylinder, and step back. Note the steam coming off the foam produced by the O2 gas.

What to Say

Pour the hydrogen peroxide into the cylinder and explain that a reaction is going on... can you see it? Probably not - even though hydrogen peroxide is constantly decomposing into water (H2O) and oxygen gas (O2), it goes so slowly that it looks like nothing is happening.

We can use a catalyst to make this reaction more exciting! A catalyst is a chemical that speeds up a reaction, but doesn't actually get used up. Think of the chemical reaction like trying to walk up big hill. It takes a lot of energy to get up that hill, so you will walk (you can act out walking up a hill). If there was a tunnel through the hill, you could walk through it a lot faster and use a lot less energy (act out easy walking). Adding a catalyst is like blasting a tunnel through a big hill - it makes the reaction go faster because it takes less energy! For older audiences, you can draw out a reaction coordinate diagram (see below).

Before you add the KI have the kids give you a 3, 2, 1 countdown. Then add the catalyst. Have them note that the “toothpaste” is smoking. The oxygen that was released is the gas trapped within the soap, making the bubbles. Depending on the age of the audience you could discuss exothermic reactions, and how they give off heat. This occurs because the water and oxygen that the hydrogen peroxide breaks down into are more stable than its original peroxide form. Therefore the excess energy is released in the form of heat. To prove that oxygen is present in the mixture you may take a glowing splint and stick it into the foam and it will light - do this with great caution!

Why It Is

The whole premise behind using catalysts is that they lower the amount of energy you need to put into a reaction for it to occur. In an uncatalyzed reaction you have to put in a significant amount more energy, activation energy, in order to initiate the reaction. However, upon the addition of a catalyst the activation energy of the reaction is lowered because the catalyst offers a different mechanism of achieving the transition state between the reactants and products. Thus, not as much energy has to be expended to convert the reactants to the transition state and then to the products.

Real Life Examples

Some products that are made in a process involving a catalyst include:

   Garbage bags
   Grocery bags
   Squeezable bottles 

These are all made from polyethylene, which is polymerizes by passing ethylene gas over a catalyst. Most other polymers are made in the same (or similar) way. Synthetic rubber, nylon, Polyester, PVC, Teflon. These are used to produce:

   bouncy balls
   pantyhose
   cell-phone and laptop cases
   rain coats
   water pipes
   non-stick surfaces and pads
   saran wrap
   food containers
   cheap wigs
   fishing line 

Catalytic converters are platinum and rhodium - based pollution scrubbers in car exhausts.

The "haber process", a well known catalytic reaction, is used to produce the nitrogen used in most modern-day fertilizer.

Laundry detergent often contain active enzymes (organic catalysts) that speed up cleaning by breaking down certain compounds.

Beer and bread are typically made with yeast, a living organism containing enzymes.

Finally, the human body itself couldn't work without enzymes – they're used by cells to grow, reproduce, and create energy.