Our world is constantly changing, as are the things in our world. Some changes that occur are the result of chemical reactions. A chemical reaction is when substances interact with one another resulting in all the substances being changed into something entirely new. Chemical reactions occur all around us, and even inside of us, every day!
There are different kinds of chemical reactions. Synthesis is when two or more different substances combine to make something completely new, like hydrogen and oxygen combining to become water. Decomposition is just the opposite. A complex substance breaks apart into it’s separate ingredients. Sea salt, used in cooking, is “made” by capturing salty ocean water and allowing the water to evaporate until all that is left is the salt (see our Evaporation experiments to learn about the water cycle). There are other types of chemical reactions that involve replacing or exchanging components, called displacement reactions. The illustration below shows how the different components interact.
Chemical reactions can be affected by other substances or variables (like reaction conditions), even if those things aren’t part of the reaction. Inhibitors slow down reactions, while catalysts speed them up. Temperature is a variable that can act as either an inhibitor or a catalyst. Cold temperatures often slow reactions down, while warmer temperatures have a tendency to speed things up.
Enzymes are biological molecules that act as catalysts in chemical reactions. There are wide range of enzymes that occur naturally in the human body that help the mechanics of our body to work. Our digestive system is full of enzymes, all designed to help convert the food we eat into the individual components our bodies need to function. One of the things that make enzymes special is that, even after the chemical reaction is over, the enzymes still remain, unchanged, ready to assist with the next reaction. In this experiment, we will examine an enzyme called catalase found in potatoes.
The Experiment
THIS EXPERIMENT REQUIRES COOKING AND THE USE OF A KNIFE. ADULT SUPERVISION IS RECOMMENDED.
Supplies: Hydrogen peroxide, a potato, 5-6 glasses or bowls, water, a knife and a cutting board, small saucepan, a spoon for adding and removing potato pieces from the glasses.
What to do: Peel and dice the potato into 1″ cubes. Add about 1/3 of the cubes to the saucepan. Add enough water to completely cover the potatoes. Cook over medium heat until the cubes are tender, about 10-15 minutes. Remove the potatoes from the heat, drain, and set aside to cool. Fill two glasses with water and four glasses with hydrogen peroxide. Make sure there is enough liquid to completely cover the potatoes once they are added. Take one raw potato cube and cut it into 4 smaller pieces. Add potato pieces to the glasses as indicated in the chart below. Observe the results.
| #1 | #2 | #3 | #4 | #5 | #6 |
| Water | Water | Hydrogen Peroxide | Hydrogen Peroxide | Hydrogen Peroxide | Hydrogen Peroxide |
| 1 Raw Potato cube | 1 Cooked Potato cube | 1 Raw Potato Cube | 1 Cooked Potato cube | 4 Small Raw Potato cubes | Save for Round 2 |
| (Control) | (Control) |
The pieces of potato in the glasses with water are there to provide a comparison. There should be no reaction that takes place in either of those glasses. Once the reaction in glass #3 has subsided, remove the potato cube and examine it. What does it look like compared to the potato piece from glass #1? After you have finished the visual inspection, add the potato piece from glass #3 to glass # 6. What happens?
What is happening: Raw potatoes contain an enzyme called catalase. Catalase is found in almost all living organisms, including people. Its job is to help speed up the decomposition of hydrogen peroxide (which can be harmful) and convert it to water and oxygen gas. The bubbles that were formed in the glasses with the raw potatoes contained oxygen gas. Just as catalase helps decompose the peroxide, heat breaks down the catalase, which is why the glass with the cooked potato piece had no reaction. Cutting the potato into smaller pieces created more exposed surfaces, giving the peroxide more opportunity to interact with the catalase. The reaction in glass #3 ended when the catalase had decomposed as much of the hydrogen peroxide as it could. Even though the potato was drastically altered visually, it still contained the catalase enzyme, which is why it could cause another reaction when added to glass #6.
Take It a Step Further
Catalase is present in almost all living organisms, so why not try this experiment with other fruits and vegetables? If you do, you can omit the cooking part, as you already know that heat degrades the catalase and makes it ineffective. The more bubbles you get in your reaction, the greater the amount of catalase present in that food. Which foods produced more bubbles? Which produced fewer bubbles?
Links
Cool Kid Facts has a great page that discusses chemical reactions and goes into more detail about some of the different kinds of reactions, including photosynthesis and combustion (did you know fire is a chemical reaction?!).
Education.com replicates this experiment, but uses raw, cooked, and frozen potatoes to compare how temperature affects the catalase. You can check it out here.
For a detailed examination of this experiment using a sweet potato and a variety of different liquids, including ammonia and vinegar, check out this chemistry class report. They have some pretty interesting pictures!