Fanelwa Ngece Ajayi
The “elephant toothpaste” experiment is a popular and visually appealing illustration of a chemical reaction that is appropriate for children.
It is the decomposition of hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2), which is catalysed by a detergent (often dish soap) and accelerated by a catalyst such as potassium iodide or yeast.
Hydrogen peroxide (H2O2) is a common household chemical that breaks down into water (H2O) and oxygen (O2) over time. The presence of a catalyst accelerates this decomposition reaction by lowering the activation energy necessary for it to occur.
In the “elephant toothpaste” experiment, a concentrated solution of hydrogen peroxide is mixed with a catalyst and detergent, causing a quick release of oxygen gas and the formation of a frothy substance resembling toothpaste.
Materials needed:
3% hydrogen peroxide solution (often found at pharmacies or supermarkets)
Dry yeast or potassium iodide (a catalyst)
Liquid dish soap functions as a detergent.
Food colouring (optional; for visual effect)
A tiny jar or bottle to store the reaction mixture.
The use of safety goggles, lab coats and gloves are advised
Safety precautions:
Goggles, lab coats and gloves should be worn at all times when carrying out the experiment because hydrogen peroxide can irritate the skin and eyes. As oxygen gas is released throughout the reaction, it should be ensured that the experiment is carried out in a well-ventilated location. Parental guidance is recommended when children conduct this experiment to ensure that they are safe at all times especially when the recommended safety wear is not available.
Procedure:
Prepare the reaction container: Place the reaction container on a flat surface that is clean and dry. A plastic or glass container is ideal for this experiment.
Add hydrogen peroxide: Pour about 100 to 150 millilitres of 3% hydrogen peroxide solution into the reaction container. You can vary the amount depending on the size of your container and the desired level of foaming. More foam is observed when more of the solution is used.
Add dish soap: Mix just a few drops of liquid dish soap to the hydrogen peroxide solution in the container. The dish soap helps to retain the oxygen gas created during the process, resulting in foam.
Optional: If desired, add a few drops of food colouring to the mixture. This can enhance the foam’s visual appeal and colour. Red or orange food colouring gives an illusion of a volcano and as such, it would be interesting to use it.
Prepare the catalyst: In a separate container, dissolve a little amount of dry yeast in warm water or make a solution of potassium iodide in water. The catalyst helps to accelerate the breakdown of hydrogen peroxide. Yeast is recommended so that children are not exposed to excess amounts of chemicals.
Add the catalyst: Carefully add the yeast solution or potassium iodide solution to the hydrogen peroxide mixture in the reaction container. Stir gently to ensure thorough mixing.
Observe the reaction: As soon as the catalyst is applied, the reaction begins. Oxygen gas will be created quickly, causing the mixture to froth and expand outside of the container. The resulting froth mimics toothpaste being squeezed from a tube, hence the name “elephant toothpaste”.
The clean-up: After the reaction is complete, dispose of the foam and remaining solution by flushing down the toilet followed by rinsing the reaction container thoroughly with water.
The “elephant toothpaste” experiment is not only entertaining for children but also provides an opportunity to discuss chemical reactions, catalysts, and the properties of gases in a hands-on and memorable way. The take-away lesson from the experiment is the observation of a decomposition reaction in which water and oxygen are the final products when hydrogen peroxide is subjected to the catalyst.
Furthermore, this experiment provides an illustration of the reduction of the activation energy known as the minimum energy required to cause a process such as a chemical reaction to occur.
This experiment is recommended for Grade 8 and Grade 9 pupils and this example is based on the South African Natural Sciences Curriculum and Assessment Policy Statement (CAPS) for Grades 7 to 9 and is available online (https://wcedeportal.co.za/eresource/112876).
- Professor Fanelwa Ngece Ajayi is a Deputy Dean: Research and Innovation and an Associate Professor of Physical Chemistry at the Chemistry Department, University of the Western Cape.
