Chemistry is an exciting subject for children of any age, especially if you set up a natural discovery environment for them to explore safely. Let’s find out how to do this in your own home with your own children. In college, one of the first things you will learn in your chemistry class is the difference between physical and chemical changes.
An example of a physical change occurs when the shape of an object changes, such as making a ball of paper. If you set the paper block on fire, you now have a chemical change. You are rearranging the atoms that used to be the molecules that made up the paper into other molecules, such as carbon monoxide, carbon dioxide, ash, etc. There is an easy way to tell if you have a chemical change. If something changes color, it emits light (like the light bars used on Halloween), or has absorbed heat (cools) or produces heat (gets hot). Some quick examples of physical changes include ripping fabric, rolling dough, stretching rubber bands, eating a banana, or blowing bubbles.
Let’s do some experiments that demonstrate the chemical changes just mentioned. The setting will look like your kitchen table covered with a plastic tablecloth. On your table there will be several bottles of clear liquids and white powders along with small measuring spoons and a tray of muffin cups.
Your mission: To find the reactions that generate the most heat (exothermic), absorb the most heat (endothermic) and which are the most impressive in their reaction (the ohhhh-ahhhhh factor). NOTE: Although these chemicals are not harmful to your skin, they can make your skin dry and itchy. Wear gloves (latex or similar) and eye protection (safety glasses), and if you are unsure about an experiment or chemical, just don’t.
Gather these together before you begin: a muffin pan, water, vinegar (acetic acid), baking soda (baking soda), washing soda (sodium carbonate), isopropyl alcohol, hydrogen peroxide, citric acid (store groceries), aluminum sulfate (“alum” in the spice section of the grocery store or the pharmacy section of the drugstore), and a clear liquid dish soap such as Ivory. Put all these items on your table.
And a head of red cabbage.
Red cabbage? Yes! Red cabbage juice has anthocyanin, which makes it an excellent indicator for these experiments. Anthocyanin is what gives leaves, stems, fruits, and flowers their colors. Did you know that certain flowers like hydrangeas turn blue in acidic soil and turn pink when transplanted into basic soil? This next step in the experiment will help you understand why. You will need to remove the anthocyanin from the cabbage and give it a more useful shape, as a liquid “indicator”.
Prepare the indicator by coarsely cutting the head of red cabbage and boiling the pieces for five minutes on the stove in a pot filled with water. Carefully strain all the pieces (use gauze if you have one) and the reserved liquid is your indicator (it should be purple in color). When you add this indicator to different substances, you will see a range of colors ranging from hot pink to tangerine orange, bright yellow, emerald green, ocean blue, and velvety purple. Try adding drops of indicator to something acidic, like lemon juice, and see how different the color is when you add indicator to a base, like baking soda mixed with water.
Put your liquid chemicals in easy-to-pour containers, like water bottles (be sure to label them, since they look the same!): Alcohol, hydrogen peroxide, water, vinegar, and dish soap. (Avoid peroxide and alcohol with young children.) Place small bowls (or zippered bags if you’re doing this with a crowd) of the powders with “scoops” made from the tops of your water bottles: baking soda, sodium carbonate, citric acid, ammonium nitrate, chloride calcium and alum. The little “spoons” regulate the amounts you need for a muffin-sized reaction.
Have your indicator in a bottle by itself. Old bottles of soy sauce or other bottles with a built-in regulator that keeps the drip is perfect. You can also use a container with a pear syringe, but cross contamination is a problem. Or not, depending on whether you want the children to see the effects of cross contamination during their experiments. (The indicator bowl will continually change colors throughout the experiment.)
The experiment: Start mixing it up! When I personally teach this class, I let them have all the chemicals at once (even the indicator) and of course this leads to a chaotic mix of everything. After the initial burst of enthusiasm, students will inherently start asking better questions. They will want to know why your cold green goo is crawling on the ground with your neighbor’s oozing a hot pink liquid, apparently with the same substance. Let them discover a system for remembering which chemical goes where and which one to get the reaction they are looking for.
Periodically hold your hand under the muffin cups to test the temperature. Use the indicator before and after mixing the chemicals, and you will be amazed and dazzled by the results! Enjoy!