A "rubber egg" is made by soaking a raw egg with its shell still intact in regular household vinegar for a specified length of time. In 2 to 3 days the egg shell will be completely dissolved by the vinegar, leaving behind the egg cell membrane, which will have taken on a rubbery consistency that holds the egg together.
The shell of an egg is made of calcium carbonate, which is the same composition as that of limestone. The acetic acid in vinegar reacts with the calcium carbonate shell to produce carbon dioxide gas and dissolved salt. This reaction gradually wears away the hard shell of the egg until it is completely gone. The "rubber egg" science experiment is a favorite among elementary students all over the world and it is often conducted to demonstrate the importance of calcium for the bones and teeth.
To make a rubber egg, one will need the following:
- A raw, preferably fresh egg
- A container large enough to contain the egg
- Enough vinegar to cover the egg completely
Place the egg inside the container gently. Make sure that the egg shell and the membrane are intact.
Pour the vinegar into the container until the egg is completely submerged. Bubbles may already start forming on the shell of egg a few minutes after pouring in the vinegar. Set aside for 2 to 3 days.
After 2 to 3 days, the egg shell will have completely dissolved, leaving a muck floating on the surface of the vinegar. Pour out the vinegar and gently take out the rubber egg.
The rubber egg experiment also demonstrates the semi-permeable properties of the egg membrane, which allows the vinegar to pass through the membrane freely. This same experiment can also be done with chicken bones with the same result, although it may take a few more days to fully dissolve the calcium in the bones.