Step 2: In the other jar fill it with enough vinegar so that the egg will be completely covered. For fun stir in some food coloring (optional). Carefully place the second egg in the vinegar. If using a jar close the lid. Label this jar "Vinegar."
What has happened is called a chemical reaction. The acid (vinegar) reacts with the calcium carbonate of the eggshell. The reaction makes the shell go soft, then disappear. This is called "decalcification".
The water is not acidic and will not dissolve the calcium in the shell. It remains unchanged (not edible but unchanged)
More vinegar fun: You can make chicken bones soft too. You can make them soft enough to bend. Put a clean wishbone or leg bone into a jar of vinegar. Make sure the bones are completely covered. Leave them alone for 7 days. The bones will go soft enough to twist them into a knot. The vinegar reacts with the minerals in the bones that make them strong and rigid. The vinegar will dissolve the minerals like it did with the calcium in the egg shell.
Who says science can't be fun?
My boys really love science experiments. They had a lot of fun with this one and yes we are soaking chicken bones as we speak. The first time we only did one egg in the vinegar. When it came time to bounce the eggs, it was over far to quick for them. They were ready to start the process all over again. The second time around we skipped the egg in the water. What we really wanted was to bounce the egg. My youngest got a little over excited when it was his turn to drop the egg. He ever so slightly threw the egg (not quite a throw and not just a drop). The force was enough to make the egg splat before we could get very many bounces out of it. For this reason I highly recommend you put two eggs in the vinegar jar (especially if you have more than one child). Not to mention you will have fun as well. I found I was just as excited to see the results as they were the first time. This experiment is just one of many that my boys have enjoyed. I hope you try this and I hope you add food coloring for a ramp up to Easter. I didn't stress the chemistry lesson here for my boys. I asked them questions to make them think a little and they asked me a whole bunch of questions about what happened and why it worked. I let their curiosity be my guide.
I also must warn you. My oldest wanted to keep the bouncy egg and to put it away with his toys. So watch that the eggs don't go missing. I explained that the egg would not last forever and that it would make a mess of his toys when it broke.