By now you've probably tried making bouncy balls... but bouncy eggs?
Making bouncy eggs demonstrates how two chemicals can interact, in this case how acetic acid (vinegar) dissolves the calcium carbonate in an egg shell. Once you have dissolved the shell, the membrane which lined the shell will remain. This makes the egg feel rubbery and bounce (when dropped from a low height).
You can do this with both boiled and raw eggs. The boiled ones are a little safer to bounce!
To make a bouncy egg place your boiled or raw egg in a small glass or jar, and cover it with vinegar. You will immediately see bubbles forming over the shell, as the calcium carbonate begins to dissolve and release carbon dioxide.
Cover the top of the jar or glass, and place it in the fridge. You'll need to change the vinegar after 24 hours or so. It will take 2-3 days to completely dissolve the egg shell.
Once the egg shell is dissolved, and the egg feels rubbery and squishy, remove it from the vinegar and dry it completely.
Then test out the bouncy egg! Drop it from a low height - the membrane will still break and you'll get raw egg everywhere. The boiled eggs work a bit better and are slightly more robust, though I still wouldn't drop them from very high!