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The Naked Egg

Question:
What do an egg shell, a sea shell and your arm bone have in common?


Answer:
They all contain calcium carbonate, a substance that makes them very hard. In this egg-speriment, you will find out how to make calcium carbonate disappear!

Question: How can you get an egg shell off without breaking the egg?

Materials:

  • 2 eggs
  • 500 mL (2 cups) vinegar (and some extra… just in case)
  • 1 clear jar (clean jelly, olive, or pickle jars work) or glass
  • Clock or timer
  • Adult helper

Procedure:

  1. Being careful not to crack the eggs, carefully place them in the jar or glass.
  2. Pour enough vinegar over the eggs until they are completely covered (if 500 mL of vinegar is not enough, add more until covered).
  3. Watch the eggs for about five minutes. Observe the bubbles of gas that are formed on the surface of the eggs; you'll notice that lots more will appear with time. Let them sit overnight.
  4. The next day, remove the eggs from the jar or glass and rinse them under a trickle of water in the sink while gently rubbing the shell with your fingers. If the shell does not come off completely, return the eggs to the jar or glass, and try again to rinse them the next day. It may take two or three days to remove the shell completely.
  5. Once the shell is gone, examine the eggs carefully. Hold the eggs up to a bright window or light. You will see the yolk as a dark blob inside. Turn the egg upside down. Can you see the yolk "sinking" to the bottom of the egg?
  6. If you want to do something really cool with the "shell-less" eggs, use them for "The Naked Egg - Part 2" egg-speriment.


What Happened - and Why?

Egg shells contain something called "calcium carbonate." This is what makes them hard. Vinegar is an acid known as acetic acid. When calcium carbonate (the shell) and acetic acid (the vinegar) combine, a chemical reaction takes place and carbon dioxide (a gas) is released. This is what the bubbles are made of.

The chemical reaction keeps happening until all of the carbon in the shell is used up - this takes about a day. When you take the eggs out of the vinegar, they are soft because all of the carbon escaped out of the shell in those little bubbles.

The egg still stays together and doesn't fall apart because it has an "invisible membrane on the surface of it which does not react with the vinegar.

Now you know how to remove the egg shell without breaking it!

The Naked Egg Part 2

Shell-less eggs or "naked eggs" are amazing. Amaze your friends or family even more when you change the shape and size of "naked eggs." Don't believe it? Try it!

Question: Can an egg change its size or shape?

Materials

  • 2 small clear jars (clean jelly, olive, or pickle jars work) or glasses
  • 2 "naked eggs" (from The Naked Egg - Part 1 above)
  • Clear (white) corn syrup
  •  Water
  • Clock or timer
  • Adult helper

Procedure:

  1. Fill one jar or glass about half-full with clear corn syrup and fill the other with water.
  2. Gently place one of the naked eggs in the corn syrup and the other one in the water. Don't be surprised if the eggs float or sink. Take a close look at the size of the egg when you begin the egg-speriment and compare it to the size of the egg two hours later.
  3. Leave the eggs in the corn syrup and water in a safe place for three days. After three days, remove them and rinse them under a trickle of water in the sink.

What Happened - and Why?

Both eggs will look very different than any eggs you've ever seen before. What you see is due to a process called osmosis. Osmosis is a process that equalizes - or makes the concentration of water on both sides of the egg membrane the same. (The membrane is an invisible covering between the egg shell and the egg itself.)

Since corn syrup has a lower concentration of water than an egg does, the water in the egg moved out of the egg causing the egg to "shrink." The egg in the water expanded or got bigger, because there was a greater concentration of water outside the egg membrane, which caused the water to move into the egg. That's why this egg is bigger than the egg you started with in the first "Naked Egg" egg-speriment.

Source: Adapted from http://www.kidzone.ws/science/egg.htm