Elephant's toothpaste

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Elephant's toothpaste is a foamy substance caused by the rapid decomposition of hydrogen peroxide by using potassium iodide as a catalyst. How rapidly the reaction proceeds will depend on the concentration of hydrogen peroxide. Because it requires only a small number of ingredients and makes a "volcano of foam", this is a popular experiment for children to perform in school or at parties; the experiment is also known as the "marshmallow experiment", but isn't related to the psychological Stanford marshmallow experiment.

Video Elephant's toothpaste

Explanation

Description

About 50 ml of concentrated (>30%) hydrogen peroxide is first mixed with liquid soap or dishwashing detergent. Then, a catalyst, often around 10 ml potassium iodide solution or catalase from baker's yeast, is added to make the hydrogen peroxide decompose very quickly. Hydrogen peroxide breaks down into oxygen and water. As a small amount of hydrogen peroxide generates a large volume of oxygen, the oxygen quickly pushes out of the container. The soapy water traps the oxygen, creating bubbles, and turns into foam. About 5-10 drops of food coloring could also be added before the catalyst to dramatize the effect. How rapidly the reaction occurs will depend on the concentration of hydrogen peroxide used.

Chemical explanation

This experiment shows the catalyzed decomposition of hydrogen peroxide. Hydrogen peroxide (H₂O₂) decomposes into water and oxygen gas, which is in the form of foam, but normally the reaction is too slow to be easily perceived or measured:

${\displaystyle {\ce {2H2O2 -> 2H2O + O2 (^)}}}$

In normal conditions, this reaction takes place very slowly, therefore a catalyst is added to speed up the reaction, which will result in rapid formation of foam. The iodide ion from potassium iodide acts as a catalyst and speeds up the reaction while remaining chemically unchanged in the reaction process. The iodide ion changes the mechanism by which the reaction occurs:

${\displaystyle {\begin{array}{llllll}{\ce {H2O2}}&+\ {\ce {I-}}&{\ce {->H2O}}&+\ {\ce {IO-}}\\{\ce {H2O2}}&+\ {\ce {IO-}}&{\ce {->H2O}}&+\ {\ce {O2}}{\uparrow }&+\ {\ce {I-}}\\\hline {\ce {2H2O2}}&&{\ce {->2H2O}}&+\ {\ce {O2}}{\uparrow }&&\Delta rH^{\circ }=-196{\text{ kJ/mol}}\end{array}}}$

The reaction is exothermic; the foam produced is hot. A glowing splint can be used to show that the gas produced is oxygen. The rate of foam formation measured in volume per time unit has a positive correlation with the peroxide concentration (v/V%), which means that the more reactants (peroxide concentration) the faster the rate of foam formation.

Maps Elephant's toothpaste

See also

• Carbon snake
• Black snake (firework)
• Diet Coke and Mentos eruption

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References

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External links

• The Elephant's Toothpaste Experiment sciencebob.com

Source of article : Wikipedia