During the summer or even after school you can do simple science experiments using lemons with kids ages 7 to 12. Lemons are inexpensive and readily available to use in supermarkets and food stores. The two experiments featured here are invisible ink and blowing up a balloon. When performing the experiments, supervise your kids, and have all supplies ready before you begin. The experiments are relatively easy and safe to perform.
Learn to write a secret message using lemon juice. Collect the following items: 1/2 lemon, small plastic bowl, cutting board, knife, spoon, cotton swab, 8 1/2 by 11 white paper, lamp with bulb. On the cutting board cut the lemon in half with a knife. Squeeze the lemon juice into the plastic bowl. Remove any seeds with plastic spoon. Discard the seeds in the trash. Add a few drops of water to the lemon juices, and mix well.
Dip the cotton swab in the lemon mixture and write a message on the white paper. Let the lemon juice dry. It will be invisible. To read the message, hold the white paper over a lamp. Remove the lampshade of the lamp and turn on the lamp. Take the paper and put it near the lightbulb, but do not let it touch. The heat from the lightbulb will make the message appear. After you finish, turn off the lamp and put the shade back on it. Clean up the area.
Understand what just happened. Lemon juice contains compounds of carbon dioxide that is colorless when dissolved in water. When heated, they produce carbon, which is black. That is why you can read the invisible message. Be careful not to burn the paper when passing it near the lightbulb. Practice safety when performing these experiments.
Gather a balloon, a measuring cup for an ounce of water, an empty plastic soda bottle, 1 tsp. baking soda, a plastic drinking straw, one lemon for juice and measuring spoon, cutting board and sharp knife. Cut the lemon with the knife on the cutting board on a flat surface like the counter or table. Squeeze juice into a plastic cup and remove the seeds with the spoon. Discard the seeds in the trash. Stretch the balloon over the bottle to make sure it fits. Then remove the balloon.
Pour the water into the clean, empty soda bottle. Add the baking soda and stir with straw. Add the lemon juice quickly, then put the balloon over the top of bottle. The balloon will inflate because the baking soda and lemon acid create carbon dioxide. Be sure to clean up after the experiment.