Compare your transformed egg to a regular egg. What do you think happened to the eggshell? What other differences can you observe? What's Going On? If you look closely at the egg while it's submerged in the vinegar, you can see bubbles forming on the surface. Those bubbles are full of carbon dioxide, just like the bubbles in a glass of soda. You're seeing a reaction between a compound in the eggshell (calcium carbonate) and an acid in the vinegar (acetic acid). This reaction creates carbon dioxide (and some other things) and breaks down the eggshell in the process. The membrane underneath the shell doesn't react, so it's left behind. Once the shell is completely gone, all that's left is the flexible membrane, giving you a bouncy "rubber" egg!