Introduction: Amaze a Science Class With Elephant Toothpaste
This experiment shows the decomposition of hydrogen peroxide catalyzed by potassium iodide. The reaction is done in a tall graduated cylinder so that the foamy product shoots out very quickly in a tall cylindrical shape; hence, the name elephant toothpaste.
tall graduated cylinder (at least 500 ml)
30% hydrogen peroxide (H202)
saturated solution of potassium iodide (KI)
1. Wear safety goggles. Also, wear disposable gloves when pouring 30% hydrogen peroxide, as it is a very strong oxidant.
2. Do not stand over the graduated cylinder because steam and oxygen are produced quickly.
1. Place a garbage bag or other covering on the lab table and possibly on the floor.
2. Fill the vial containing potassium iodide with water. Cap and shake until all the potassium iodide is dissolved (This should now be a saturated solution of KI made with 15 grams of KI and water.) Set aside.
3. Put on disposable gloves. Pour 80 ml of 30% hydrogen peroxide into a graduated cylinder.
4. Add about 40 ml of Dawn detergent to the hydrogen peroxide. Swirl to mix
5. Tilt the graduated cylinder and drip red and/or blue food coloring down the sides of the graduated cylinder to make your toothpaste striped
6. Quickly add the saturated solution of KI solution and stand back Be sure to move your hand away from the top of the graduated cylinder quickly or the hot foam will get on your hand and arm.
7. You may place a glowing splint in the foam to test for oxygen, but do not drop the splint into the graduated cylinder. The splint will relight indicating the presence of oxygen.
The rapid catalyzed decomposition of hydrogen peroxide produces O2 gas which forms a foam with the liquid detergent:
2H2O2 (aq) -> 2H2O + O2 (g)
The I-1ion is a catalyst for the reaction. The brown color of the foam is evidence of iodine in the reaction. It will stain clothes, skin, and carpet
Leave the gloves on while cleaning up. The foam and solution left in the graduated cylinder may be rinsed down the drain with excess water.
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