Elephant Toothpaste
- Page ID
- 128806
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Required Training |
Required PPE |
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UC Lab Safety Fundamentals |
Lab coat, safety glasses/goggles, nitrile gloves |
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Performers Required: 1 |
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Equipment |
Chemicals |
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1 L glass graduated cylinder or other pyrex glass container |
Hydrogen peroxide (H2O2), 30% solution |
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Clear plastic tub |
Potassium iodide (KI), solid powder or sat. solution |
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Dish soap |
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Food coloring (optional) |
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Procedure:
- Place the clear plastic tub on the ground, and then place the graduated cylinder in middle of the tub.
- Pour 30 mL H2O2 into the graduated cylinder.
- Pour a few drops of dish soap into the cylinder and agitate slightly to mix.
- (optional) Run a few drops of food coloring down the sides of the cylinder for a striping effect.
- There are two methods for performing this demonstration:
- Method 1) Quickly pour ~10 mL of the saturated potassium iodide solution into the cylinder and step back, as a large volume of soap suds will very quickly erupt from the top of the cylinder and land in the plastic tub.
- Method 2) Add 0.5 g (or one scoop) of solid KI powder to the cylinder and step back. As the solid must dissolve and diffuse through the solution, this reaction is much slower and produces a stream of foam from the cylinder that may continue for up to a minute.
- This reaction produces a significant quantity of heat, and the graduated cylinder will be hot to the touch. Allow it to cool sufficiently before moving the demonstration and handle with heat-resistant gloves.
Clean-up: Once everything has cooled to room temperature, all waste can be safely rinsed down the drain.
Hazards: 30% H2O2 is corrosive and strongly oxidizing, causing immediate chemical burns on contact with skin. Always wear nitrile gloves when preparing, performing, or cleaning up this demo. Furthermore, the catalytic decomposition of H2O2 is strongly exothermic, and the graduated cylinder may become warm enough to cause thermal burns during the demonstration.
Principle: This demonstration involves the catalytic decomposition of H2O2 into water (H2O) and oxygen gas (O2(g)). The overall reaction is:
2 H2O2(aq) → 2 H2O(l) + O2(g)
This reaction is slow, but may be catalyzed by the iodide ion (I-). One proposed mechanism for this reaction is:
H2O2(aq) + I-(aq) → OI-(aq) + H2O(l)
H2O2(aq) + OI-(aq) → I-(aq) + H2O(l) + O2(g)
A significant quantity of heat is also generated (ΔrH° = −196 kJ/mol), which vaporizes some of the H2O into steam. The soap catches the evolved steam and oxygen, forming many small bubbles that coalesce into a foam.
Notes: More is going on in solution than just the reactions given in the mechanism listed above. Upon the addition of KI, the solution becomes a red-brown color that slowly clears, evidence for the formation and subsequent consumption of iodine (I2) and the triiodide (I3-) anions that form upon reaction with excess I-. Research on the reaction mechanisms and kinetics of this system is still ongoing. This demonstration is nearly identical to Genie in a Bottle, which does not use soap to catch the evolved gases. Ensure performers are aware that the food coloring may stain their shoes. Other pyrex glass containers of different shapes can be used for different foam effects..