I've decided to post a series of science experiments that parents can use with preschool children. These are the very experiments I performed as a child, although I'm only posting the safe and legal ones. In fact, these experiments might just distract the child from the more dangerous forms of experimentation.
If, by any chance, you happen to have a severely inquisitive child like I was, I'd suggest sitting down and explaining the types of experiments that will cause excruciating and long-lasting pain, either from experimenter error or parental disapproval. Getting rid of all flammable liquids might be a good idea, too.
Some of the things the child learns will be beyond their current ability to understand. These experiments, though, are memorable, and as the child's mind develops and the child grows in experience, concepts that were missed will, at some point, "click."
Please don't give your child the "needed" list and turn them loose. Work with them, so that they can play with you while doing this. When I was older, my Dad got me a chemistry set and "turned me loose." I appeared "smart enough" for that. I might have been "smart enough," but I lacked the maturity. I wish my Dad hadn't done that, and instead had worked with me and the chemistry set. I think I would have learned much more from the chemistry set if he had worked with me. There wouldn't be a chunk of concrete missing from the laundry room floor, either.
Note: Small children do not really comprehend death. Telling a child that "doing that might get you killed" means nothing. As a small child, I had an advanced understanding of my own mortality, and yet that never stopped some of the experiments it should have. While they do not understand death, they do understand pain and seek to avoid pain when possible. So, when you speak of dangers, speak of how much they will hurt, that the child may wind up in the hospital (away from mom and dad), getting "shots." You don't need to explain the difference between IVs and shots, if you don't want to.
I've always wondered: if my Dad had told me to stick the poles of a 9-volt battery on my tongue to see what it feels like to get shocked (it stings, but it's non-lethal), would I ever have stuck that wire into the electrical outlet? I am lucky I lived through that 120v "experiment," and I obviosly do not recommended that experiment.
Experiment #1
Needed: Small paper or plastic cups (you can use larger, with more mess), spoons, baking soda, vinegar, paper towels, old clothes for the child and parent(s).
Concept being taught: Matter is made of chemicals, and some of these chemicals react when brought together. You can talk about things rusting, food (made of chemicals) oxidizing in the child's body under controlled conditions, etc.
Instructions:
Explain to the child that you never contaminate large quantities of chemicals by using them directly out of the bottle or container in an experiment. This is actually why you should never crack eggs directly into a recipe, by the way. Crack them into a bowl, check to see if they're rotten, and then add. Trust this advice from someone who learned the hard way. So put some vinegar into one cup, baking soda into a second. Put separate spoons in each container, and allow the child to mix baking soda and vinegar together.
Baking soda is NaHCO3, which is a base, as you might remember. Vinegar is 4% acetic acid and water, with acetic acid's chemical formula being written CH3COOH or C2H4O2. You don't have to tell the child this. I'm explaining this so you'll know what's going on. Acetic acid is an acid (duh!), and that means it likes to give away a hydrogen ion. The baking soda will swap out the sodium for the hydrogen ion, leaving H2CO3, which can be rewritten H2OCO2. H2O, conveniently enough, is water, and CO2 is carbon dioxide, a gas. So the baking soda breaks down into carbon dioxide gas and water, and the carbon dioxide gas bubbles away! The acetic acid is turned into sodium acetate, CH3COONa. The sodium replaces the hydrogen ion the acetic acid gave up.
Let the child use larger and larger quantities of baking soda and vinegar. One good thing to try is to pour some vinegar into a cup and put tiny amounts of baking soda in. Eventually, the child will "use up" the vinegar and it will stop foaming and bubbling. Explain that the baking soda used up all the vinegar. Then, try the experiment in reverse, where vinegar is added to baking soda. Again, the baking soda gets "used up." The child will learn an intuitive version of "chemical equation balance" by this.
If your child enjoys making a mess, let the child create a small mess! That's part of the fun! If you have a neat child, don't force the child to be messy. Should they choose to be messy, though, again, let them. If, at some point, the child asks to taste the baking soda, vinegar, or the liquid left after the reaction (which contains water, sodium acetate, and either a bit extra baking soda or vinegar), explain that this is not poisonous, but it might not taste very good. On a practical level, don't let the child consume more than about a fraction of teaspoon's worth. You don't want the child spitting this stuff all over the kitchen or throwing up. Make sure the child rinses the mouth with water between tastes. Do not permit the child to mix the baking soda and vinegar in the mouth — the foam could get inhaled, which would not be good. Explain this to the child, that it's like swallowing food down "the wrong way" and that it would hurt and require a trip to the hospital, possibly with shots involved.
Have the child help clean up afterward. Explain that real scientists clean up after their experiments. This isn't always true, but one of the points of these science experiments is to create a future generation of good scientists!