Elephant's+Toothpaste+Prac

Elephant's Toothpaste

The following practical is excellent for Yr 7 and below, but be aware that Hydrogen Peroxide is toxic so care should be taken when using it. If the Yeast is not fresh it will work better with replacing the Yeast with Manganese Dioxide (black powder), or Potassium Hydroxide??

There is an excellent 5 min video on the following site along with instructions using Yeast - just replace yeast with the manganese dioxide (one tea spoon). http://www.sciencebob.com/experiments/videos/video-foam1.php



http://www.sciencebob.com/images/elephant_toothpaste.gif

The foam is made as the dishwashing detergent traps tiny oxygen bubbles created by the chemical reaction that is happening inside the bottle. The thick foam oozes out of the top of the bottle and looks like toothpaste when toothpaste is being squeezed out of its tube. The activity is called ’Elephant’s Toothpaste’ because the large stream of foam looks like toothpaste that is big enough for an elephant! Hydrogen peroxide is a molecule made up of hydrogen atoms and oxygen atoms. It can be expressed using the chemical formula, H2O2. Under the right conditions, hydrogen peroxide will undergo a chemical reaction to break down into two parts, oxygen and water. We can write out this decomposition reaction as a chemical equation:
 * hydrogen peroxide || → || water || + || oxygen ||
 * 2H2O2 || → || 2H2O || + || O2 ||

When a chemical that is made up of only one molecule breaks down into two different, smaller molecules, it’s called a decomposition reaction. This particular decomposition reaction is also an ’exothermic’ reaction, meaning it gives off heat. If you feel the sides of the bottle, the plastic should feel quite warm. Yeast contains an enzyme called catalase. The enzyme is called catalase because it works as a ’catalyst’ in this reaction. A catalyst is a substance that speeds up the rate of a chemical reaction without changing its products. The yeast is added to the hydrogen peroxide to speed up the reaction. The catalase in the yeast speeds up the process of breaking down the hydrogen peroxide and thus produces oxygen and water more quickly. The oxygen gets trapped by the dishwashing detergent as many tiny bubbles.

Try making the elephant toothpaste in different sized PET bottles or in containers with different shaped openings to determine how these affect the stream of foam. Try using different quantities of the mixtures to determine how it affects the amount of foam.