As students observe the production of gas bubbles on the shell, they may infer this as a sign of a chemical reaction.  In this case, a chemical reaction between the shell (made of calcium carbonate) and the acetic acid in the vinegar occurs.  The resulting products include calcium acetate, water, and carbon dioxide bubbles that form on the shell.

After 48 hours, you can carefully rinse the remaining products off the egg and what remains is the super cool, translucent membrane.  This super thin but super tough membrane is also semipermeable – it allows many materials to flow back and forth through the membrane according to differences in concentration.  The flow of water through a semipermeable membrane is called osmosis.  When the membrane is placed in water, water flows into it and the egg expands.  The membrane is also amazingly tough.  See how far you can drop it from before it POPS.

Key Concepts: matter, chemical reactions, osmosis, semipermeable, translucent.