This experiment answers the age-old question, “Which came first, the rubber egg or the rubber chicken?” It’s easy to make a rubber egg if you understand the chemistry of removing the eggshell with vinegar. What you’re left with is a totally embarrassed naked egg and a cool piece of science.
What you need:
- Raw egg
- Graduated cylinder or tall glass
What to do:
- Place the egg in a graduated cylinder or tall glass and cover the egg with vinegar.
- Look closely at the egg. Do you see any bubbles forming on the shell? Leave the egg in the vinegar for a full 24 hours.
- Change the vinegar on the second day. Carefully pour the old vinegar down the drain and cover the egg with fresh vinegar. Place the glass with the vinegar and egg in a safe place for a week – that’s right, 7 days! Don’t disturb the egg but pay close attention to the bubbles forming on the surface of the shell (or what’s left of it).
- One week later, pour off the vinegar and carefully rinse the egg with water. The egg looks translucent because the outside shell is gone! The only thing that remains is the delicate membrane of the egg. You’ve successfully made an egg without a shell. Okay, you didn’t really make the egg – the chicken made the egg – you just stripped away the chemical that gives the egg its strength.
Why it works: Let’s start with the bubbles you saw forming on the shell. The bubbles are carbon dioxide gas. Vinegar is an acid called acetic acid – CH3COOH – and white vinegar from the grocery store is usually about 5% acetic acid and 95% water. Egg shells are made up of calcium carbonate. The vinegar reacts with the calcium carbonate by breaking the chemical into its calcium and carbonate parts (in simplest terms). The calcium part floats around in the solution while the carbonate part reacts to form the carbon dioxide bubbles that you see.
Some of the vinegar will also sneak through, or permeate, the egg’s membrane and cause the egg to get a little bigger. This flow of a liquid from one solution through a semi-permeable membrane and into another less concentrated solution is called osmosis. That’s why the egg is even more delicate if you handle it. If you shake the egg, you can see the yolk sloshing around in the egg white. If the membrane breaks, the egg’s insides will spill out into the vinegar. Yes, you’ve made a pickled egg! Allowing the egg to react with the carbon dioxide in the air will cause the egg to harden again. Amazing!
Additional Info: Science Fair Connection
To be an effective science fair project, something has to change in the experiment. The Naked Egg experiment described above is really just a cool science demonstration because it doesn’t contain a variable, or something that changes that allows you to run more tests and make comparisons. If you want to use the Naked Egg experiment for the science fair, consider one of the following questions or, better yet, make up your own!
- Do organic or free-range eggs have an eggshell that is stronger or weaker than generic eggs? Conduct your own test on several different kinds of eggs all at the same time to observe any differences in the time required for the vinegar to dissolve the shell.
- What happens if the egg is hardboiled? Does the shell still break down in the vinegar? How does that compare to using a raw egg?
- Try using concentrated vinegar instead of traditional vinegar. Does it make a difference? If you want to cut down on the time it takes for the eggshell to disappear, try using either 1 M hydrochloric acid or 3 M hydrochloric acid. Be careful – this is really strong stuff! (Note: The acid version of the Naked Egg experiment is only recommended for teachers and other scientists.)
- What would happen if you put an egg in one glass with vinegar and then put a different object in vinegar in another glass–maybe a piece of fruit with an outer “shell” or peel like an orange? Soak the objects in the same amount of vinegar for the same amount of time and then compare the results.
Just remember that to be “Science Fair Certified,” a project must change something, create a new experiment, and then make comparisons. If you are able to do that with the variable that you choose, you should be on your way to a great project!