Chemistry is an exciting subject for kids of any age, especially if you set up a natural discovery environment for them to safely explore in. Let’s find out how to do this in your own home with your own kids. At the university, one of the first things you will learn about in your chemistry class is the difference between physical and chemical changes.
An example of a physical change happens when you change the shape of an object, like wadding up a piece of paper. If you light the paper wad 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, and so forth. There’s an easy way to tell if you have a chemical change. If something changes color, gives off light (like the light sticks used around Halloween), or has heat absorbed (gets cold) or produces heat (gets warm). Some quick examples of physical changes include tearing cloth, rolling dough, stretching rubber bands, eating a banana, or blowing bubbles.
Let’s do some experiments that demonstrate the chemical changes we’ve just mentioned. The setup will look like your kitchen table covered with a plastic tablecloth. On your table 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 cause your skin to dry out and itch. Wear gloves (latex or similar) and eye protection (safety goggles), and if you’re not sure about an experiment or chemical, just don’t do it.
Gather these before you start: a muffin cup baking tray, water, vinegar (acetic acid), baking soda (sodium bicarbonate), washing soda (sodium carbonate), rubbing alcohol, hydrogen peroxide, citric acid (grocery store), aluminum sulfate (“alum” in the spice section of the grocery store or in the pharmacy section of the drug store), 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 to a basic soil? This next step of the experiment will help you understand why. You’ll need to get the anthocyanin out of the cabbage and into a more useful form, as a liquid “indicator”.
Prepare the indicator by coarsely chopping the head of red cabbage and boiling the pieces for five minutes on the stove in a pot full of water. Carefully strain out all the pieces (use cheesecloth if you have it) and the reserved liquid is your indicator (it should be purple). When you add this indicator to different substances, you will see a color range anywhere from hot pink to tangerine orange to sunshine yellow to emerald green to ocean blue to velvet purple. Try adding drops of indicator to something acidic, such as lemon juice and see how different the color is when you add indicator to a base, like baking soda mixed with water.
Set out your liquid chemicals in easy-to-pour containers, such as water bottles (be sure to label them, as they all look the same!): alcohol, hydrogen peroxide, water, vinegar, and dish soap. (Skip the peroxide and alcohol with small kids.) Set out small bowls (or zipper bags if you’re doing this with a crowd) of the powders with “scoopers” made of the tops of your water bottles: sodium bicarbonate, sodium carbonate, citric acid, ammonium nitrate, calcium chloride, and alum. The small “scoopers” regulate the amounts you need for a muffin-sized reaction.
Have your indicator in a bottle by itself. Old soy sauce bottles or other bottles with a built-in regulator that keeps the pouring to a drip is perfect. You can also use a bowl with a bulb syringe, but cross-contamination is a problem. Or not – depending if you want kids to see the effects of cross-contamination during their experiments. (The indicator bowl will continually turn different colors throughout the experiment.)
The Experiment: Start mixing it up! When I personally teach this class, I let them have at 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, the students will intrinsically start asking better questions. They will want to know why their cold green goo is creeping on the floor with their neighbor’s just oozed together a hot pink liquid, seemingly with the same stuff. Let them figure out a system of remembering which chemical goes where and with which 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 you mix up chemicals, and you will be surprised and dazzled by the results! Enjoy!