This time we are going to talk about a very important substance, oxygen. Oxygen is the third most abundant element in the universe, coming after hydrogen and helium. About 20% of the air around you is made up of oxygen, and it is vitally important to life on Earth. It is also important for combustion, and that is what we will explore today.
You will need:
- a long wooden skewer
- a lighter
- 3% hydrogen peroxide (from the grocery or pharmacy)
We have seen in past experiments that if you cover a burning candle with a glass container, it will go out when it runs short of oxygen. This time we are going to see how having extra oxygen effects the way things burn. To get the extra oxygen, we will start with some hydrogen peroxide.
Sprinkle some of the yeast into the peroxide and give it a stir. Very quickly you will see bubbles rising, producing foam on top of the liquid.
Light the end of this bamboo skewer, and let it burn for a moment. Then blow out the flame. It is still burning, but not flaming. If you blow gently on the burning end, you should see a red glow. Carefully bring the glowing end of the skewer up to the larger bubbles in the foam. The skewer should flare up, bursting into flame.
Why does that happen? Hydrogen peroxide has the chemical formula H2O2. That looks very similar to the formula for water, and it is. In fact, we can convert it into water by causing it to give off the extra oxygen.
One way to do that is with an enzyme called catalase. Catalase is found in human cells, which is why this stuff bubbles when you put it on a cut. Those bubbles do not indicate any infection or germs. Instead, they tell you that some of your cells have been damaged, which you probably already know if you are using the hydrogen peroxide. Catalase is also present in yeast, so when you sprinkle yeast into the hydrogen peroxide, you get bubbles of oxygen. When you bring the burning skewer near the bubbles, the extra oxygen causes it to burn very quickly.