In this activity: chemistry; states of matter; chemical reactions; semi-permeable membranes; osmosis
In this simple and fun activity, we explored chemical reactions and the different parts of an egg.
Step 1: Dissolve the eggshell
Soak an egg in vinegar to dissolve its shell. This may take anywhere from 12 hours to a few days, depending on the thickness of the shell. You can also experiment with speeding up or slowing down this process by comparing how long it takes an eggshell to dissolve in warm, cold, and room temperature vinegar.
How it works: Eggshells are mainly composed of calcium carbonate. The acetic acid in the vinegar will react with the carbon, breaking its bond with the calcium and dissolving the shell. Your little scientist can immediately observe small bubbles forming on the shell. These are carbon dioxide, a product of this reaction. After some time, you’ll also notice a white foam forming on top of the vinegar, which is the calcium that has been released along with other components of the eggshell.
Step 2: Make some observations
Once the shell has dissolved completely, use your senses to investigate! What does the egg feel like? How does it look? How does it smell? (Spoiler: It smells like vinegar!)
Hold your egg up to a bright light and notice its different parts. You should be able to clearly see the yolk. Since it is denser than the egg white, it will sink to the bottom as you rotate the egg. Hopefully, you do not see a little chicken staring back at you!
How it works: With the shell gone, your egg is now being held together by two thin layers of membrane. It may feel a bit like a water balloon to you. (Pro tip: It is not as strong as a water balloon, so use your gentle fingers.)
Step 3: Color your egg
Soak your egg in water with food coloring of your choice. We let ours sit overnight. As you can see, in addition to coming out a roaring blue, our egg also swelled to about twice its original size!
How it works: The membrane beneath an eggshell is called “semi-permeable,” meaning some substances can travel through it and some can’t. While it does an excellent job of holding in the yolk and all those gooey proteins in the albumen, or egg white, this thin barrier allows other substances — such as air and water — to pass into the egg. Did you ever wonder how a baby chicken breathes in there before it hatches?
The inside of an egg is about 90% water. When the egg is submerged, there is a higher concentration of water molecules outside of the membrane (100%), so water molecules pass through the membrane into the egg in order to balance out this difference. This process is called osmosis.
Next level: Make a hypothesis
What do you think will happen if you submerge your egg in corn syrup, which is only about 25% water? Make a hypothesis, test it, and explain what you observe!
Wrap up: What’s really inside?
You knew it had to end this way! When you’re done experimenting with your egg, break the membrane and check out the insides. As you can see, the blue color on our egg was not just on the membrane. The food coloring passed through the membrane to color the albumen, and so much water passed through that the proteins in the albumen have become diluted. Instead of the clear goo we would expect to find, we have a yolk swimming in a pool of blue water!
Can you see the two different layers of membrane that separated when our egg was broken?
Your turn! What other experiments can you do with the parts of an egg? Let us know in the comments! We can’t wait to hear what you come up with!
