Disappearing egg shell

I've seen a few people posting on social media about dissolving egg shells to make 'bouncy eggs'. Whilst this is quite neat, I can't justify wasting an egg, so I wanted to find a different way to show my son the same intriguing science.

Half egg shell

The egg shell is made of calcium carbonate (just like limestone) and you can make this 'disappear' using a chemical reaction with vinegar. The vinegar contains acetic acid, which reacts with the calcium carbonate to form soluble calcium acetate (which dissolves in the vinegar) and carbon dioxide gas.

Half shell immersed in vinegar

We had used an egg in baking, so I kept and washed the broken shell. This experiment would have been done with both halves, except that my son was too interested in the broken egg and wanted to feel it and see how strong it was, and the answer was that it cracked very easily in his hands... he learnt that eggs are stronger when they are intact! Anyway, it worked just fine with only half and he got to clearly see the membrane inside the shell too.

Bubbles of carbon dioxide

We put the remaining half in a glass jar and covered it with white vinegar. We watched it for a few minutes, seeing it start to fizz. We talked about what was in the bubbles (carbon dioxide) and how there must be some kind of chemical reaction happening. I suggested maybe the eggshell would be gone by the next morning, but my son was sceptical...

The shell has gone, leaving membranes behind

The next morning, the small boy was impressed to see the egg shell had lost its shape and had mostly gone (aside from a few fragments which seemed to have floated on the bubbles and not been immersed in the vinegar). We gave what was left a poke - making sure the few remaining bits of shell were submerged -  and found it was all floppy ("squidgy" as my son described it).

All that was left

We left it another few hours and came back to find all the shell had gone. My son tried to use some tweezers to fish the remaining membrane and coloured layer from the outside of the egg out, but it was a bit tricky to squeeze them hard enough so he asked me to help.

We had a brief look at what was left and he concluded the egg shell had become invisible. He's not wrong - it's no longer visible, having reacted with the vinegar to become part of other molecules either dissolved in the liquid or released into the air. It wasn't quite as impressive as producing a bouncy, shell-free egg, but it still showed an interesting chemical reaction!