Did your mom ever pour hydrogen peroxide on a cut when you were younger? It bubbled up and made you cry because it felt like burning and stinging but mom promised it was going to make your cut "all better". Turns out mom was lying about it helping your cut, most evidence suggests that it does little to disinfect a wound. But, it was cool to look at with all those bubbles coming out of your skin! The real questions it, why does hydrogen peroxide bubble when you put in on a cut?
Why does hydrogen peroxide bubble on a cut?
Hydrogen peroxide has the chemical formula H2O2 which means it is very similar to water, H2O, with an extra oxygen added to it. Hydrogen peroxide naturally breaks apart into water and oxygen on its own, this is called a decomposition reaction, but it happens very slowly.
Animals, including humans, have an enzyme in their body called catalase. An enzyme is a biological catalyst, which means it speeds up or slows down a reaction inside the body. The catalase enzyme speeds up the decomposition reaction of hydrogen peroxide inside the body. Why do we have hydrogen peroxide in our bodies? It is produced naturally when cells extract energy from food. This process is called metabolism. This byproduct of metabolism is harmful to your cells so the enzyme catalase is needed to quickly break down the hydrogen peroxide into water and oxygen - thus keeping the cell healthy.
The liver has very high concentrations of the catalase protein. When hydrogen peroxide is dripped on liver it comes into contact with the catalase and we can see the visible decomposition reaction occur.
Elephant Toothpaste Demonstration
The biological catalyst, catalase, speeds up the decomposition of hydrogen peroxide fairly quickly but there are chemical catalysts that cause the reaction to occur much more rapidly. Potassium Iodide (KI) is one such chemical catalyst. The Elephant Toothpaste demonstration, which is also commonly called Old Foamy, shows this reaction very well.
How to make elephant toothpaste: (click supplies for ordering information)
Pour 40 ml of dish soap into a large graduated cylinder or large beaker. Mix 10 g of potassium iodide and 5 ml of water together in a small beaker. In a separate beaker, measure 50 ml of hydrogen peroxide. Drip food coloring down both sides of the graduated cylinder so the toothpaste will have colored stripes. Pour potassium iodide/water mixture into the large graduated cylinder and, at the same time, pour in the hydrogen peroxide.
Stand back and watch the reaction produce a huge column of soapy bubbles that rises up and spills out onto the table. The bubbles are the products of the reaction: water and oxygen gas. The yellow color is from the iodine in the potassium iodide.
Hydrogen peroxide reaction equation (Decomposition)
H2O2 --> H2O + O2
Hydrogen peroxide reaction balanced chemical equation
2H2O2(l) --> 2H2O(l) + O2(g)
**Warning: 30% hydrogen peroxide is very harmful. This experiment should not be performed by children and protective gloves, apron, and googles should be worn at all times**
Craig Beals visits the news crew at KTVQ on Montana This Morning to host the Science Spot and share the awesome science behind hydrogen peroxide and Elephant Toothpaste (watch here).