5 Hands-On Experiments to Teach Kids About Chemical Reactions
What is Chemistry?
Chemistry can be defined as the study of matter and how that matter undergoes change. That is a pretty boring definition that leaves out all the fun and excitement that comes with studying chemistry. Chemistry is all around you; it explains baking and why an apple turns brown when cut open. Chemistry is the secret behind some magic tricks and colorful fireworks. So when you teach your students or children about chemistry move away from using textbooks, because this subject is best learned by observation and hands on experimentation.
What is a Chemical Change?
A chemical change is when 2 substances are mixed together to form something new. This differs from a physical change, which is a substance changing physical forms but still retains its original properties. Sometimes when a mixture is made it can be hard for kids to tell if a chemical change has occurred. Such as when mixing sugar and water, the sugar appears to be no longer present so children assume a chemical change has happened when in reality the mixture can be separated back into it's original substances. There are 4 main clues that a chemical change has occurred.
- There is a formation of gas which can be seen by a fizzing or bubbling
- The reaction will cause heat, light or odor to be emitted
- A color change is produced
- A solid is formed during the change
These are good questions to have kids ask themselves while doing the experiments to help them to determine if a chemical change has occurred or if it is simply a physical change.
One note before I move on to the activities. Make sure when you do scientific activities of any kind to go ask questions, go through the scientific method and have them form a hypothesis and discuss if they were correct at the end. It's good practice for more advanced science and it gets the mind working.
1. The first experiment is a very simple one that shows children how to tell if a chemical reaction has occurred by observing the formation of a gas.
- A bottle
- baking soda
- a balloon
- a funnel
Have the kids place a small amount (a couple tablespoons) of baking soda in the balloon using the funnel. Then have them pour vinegar into the bottle so it is about half full. Very carefully stretch the balloon around the top of the bottle, making sure you keep the balloon down so that the baking soda doesn't fall into the bottle just yet. Once the kids have formed their guesses have them tip the balloon up to allow the baking soda to drop into the bottle. Make sure they hold the top of the balloon so that it doesn't come off. Once they have observed the reaction, ask questions. What type of reaction occurred? How do they know? What is inside the balloon?
2. Next we have an experiment that shows how a chemical reaction can produce heat.
- 1 tsp of yeast
- 1/4 cup of hydrogen peroxide
- a stirring stick
- a thermometer
- a bowl
Pour the peroxide into the bowl and place the thermometer in the liquid. Let it sit for a few minutes until the temperature has stabilized. Have the kids record this starting temperature. Now have them make their guess as to what will happen and if it will be a chemical or physical change. Pour in the yeast and stir. The mixture should start to fizz and bubble which is a clue to the fact that a chemical reaction is happening, but have the kids keep their eye on the thermometer. They can also touch the outside of the bowl to physically feel the temperature change. Have them record the temperature the end. Were they right? What type of change occurred? What made the temperature rise?
3. Next up is the formation of a solid. You can also use baking as an example for this- bread is formed and cannot be separated back into flour and water, but this one is more fun.
- 3/4 cup of warm water
- 1 cup of glue
- a large bowl
- a cup
- an additional 1/2 cup of warm water
- 2 tsp borax
- a spoon
Adults: Place the 1/2 cup of warm water into a cup and stir in the 2 tsp of borax
Have the kids pour the water and glue into the bowl and stir them together. Ask them for any observations. Then have them stir while slowly pouring in the borax solution (this is a good 2 person job). Have them keep stirring until the solid forms completely. Ask for their observations. Did a chemical change occur? How do they know? This is fun experiment with a fun outcome so don't forget to let them play with the new substance for awhile!
4. The last thing to look for when trying to tell the difference between and chemical and physical reaction is the occurrence of a color change.
- 3 test tubes with lids (or any container) filled half full with water
- food coloring
- 3 containers: 1 containing bleach, 1 containing vinegar, 1 containing hydrogen peroxide
- 3 droppers
Have the kids drop a couple drops of food coloring into each of the tubes containing water. Tell them you are going to add a different liquid to each of the 3 tubes of colored water and they have to decide if a chemical change happens or not. Have them take one dropper full of the vinegar and add it to one of the colored tubes. Cap and shake, or stir, the tube. Allow them to make any observations before repeating this process with the remaining 2 liquids and tubes. The bleach will produce a change in color indicating that a chemical change has occurred.
5. And finally, here is an activity that can either be done as a demonstration or done by the kids on a smaller scale. It's called elephant toothpaste and it's even better than the exploding baking soda and vinegar. It also shows an example of a reaction that is both exothermic (gives off heat) and produces a gas.
- an empty plastic soda bottle (about 16 oz)
- 1/2 cup of hydrogen peroxide ( the 3% version you can get at the store)
- 1 pkg of yeast
- 1/4 cup of warm water
- dish soap
- a cup
- optional: food coloring
Adults: Pour the peroxide into the bottles
Have the kids place a few drops of food coloring into the bottles with the peroxide. Add a squirt of dishsoap and swirl the bottle to mix. In the cup, mix the water and yeast and stir for a few seconds to combine. Then have them pour the yeast into the bottle with the peroxide and watch what happens! Once the reaction has completed, they can feel the foam and observe the heat that was created. What did they observe? What are the clues that a chemical change occurred?
*Note: if you want to make this a demonstration, you can use a higher percentage hydrogen peroxide. You can find 6% at beauty supply stores. And sometimes even higher online. The resulting reaction will be much bigger and more impressive, but should be done completely by an adult.