Hydrogen Peroxide (6% works best, but in the video below we used a 3% solution)
Liquid Dish Soap.
Begin by pouring 1/2 cup of hydrogen peroxide into a 20 oz pop bottle (or 1 liter as we did). Drop a few drops of food coloring into the bottle as a simple way to color the 'toothpaste'. Be careful with the hydrogen peroxide as it can burn your skin. An adult should definitely be the one to handle this step. Squirt about 1 tablespoon of dish washing soap into the bottle.
In a separate bowl mix 1 tablespoon of yeast and 3 tablespoons of water water. Mix until the yeast dissolves.
Now carefully poor the yeast/water mixture into the pop bottle and watch what happens.
We used a 3% hydrogen peroxide solution and as you can see from the video it worked, although the reaction was slow moving. A 6% hydrogen peroxide solution will improve the dramatic effect by increasing the reaction time. My daughters still enjoyed it, however! Give it a try on your own. It's a great rainy day/weekend activity!