Bouncy Eggs?

Every look at your bouncy ball and wonder what gives it its bounce? A rubber band its stretch? A plastic bottle its hardness? Today, using just hard boiled eggs, we can learn all about the structures of different rubbers and plastics. Bet you didn’t think we could make an egg bounce! As a side note we are going to peel a raw egg without ever cracking it, it will bounce too!

What you will need:

11 eggs
2 quarts of water

2 cups vinegar

1 large pot (1 to 2 gal is great!)

Black marker
A large knife (caution! Remember to get an adult to help when using knives or stoves!)
Kitchen timer
A slotted spoon
Large bowl of ice and water

Remember, it is best to gather all of your equipment first. That way you won’t have to search for it while you are conducting experiments and you won’t run out of ingredients after you have started.

The experiment is best done in two. days. Steps 1 and 2 can be completed in less than an hour on the first day. After about 24 hours (or the next day), steps 3 and 4 on the experiment can be completed in about 30 minutes.

Step One

Place 1 egg in a container large enough to hold all of the vinegar. Cover the egg with the 2 cups of vinegar and leave the container uncovered overnight or for about 24 hours. Occasionally you can take a look at the egg to see what is happening. Go ahead and feel it too. Notice if you rub off all the bubbles the egg sinks, then bubbles form and the egg floats again. We will talk more about what is happening at the end.

Step Two

In your large pot bring the 2 quarts of water to a low boil. Caution! Remember to find an adult helper when using the stove!

While you wait for the water to boil, use the marker to number 6 eggs 1 through 6. If you mark the wider end of the egg that end will point up and you can see the numbers as they cook. Number the remaining 4 eggs 3 through 6. Once your water is boiling, carefully using a slotted spoon, place all eggs in the water, keep the water at a boil. Start your timer for 5 minutes.

At 5 minutes pull out egg number 1 using your slotted spoon. Restart your timer for another 5 minutes. After another 5 minutes pull out egg number 2. Repeat this at 5 minute intervals until all of your eggs have been removed from the water. You can pull out both number 3’s, 4’s , 5’s and 6’s at the same time. The eggs marked 6 should have cooked in low boiling water for 30 minutes. Allow the eggs to cool completely in the ice water, remove them and then refrigerate overnight.



Step Three

Once your egg in vinegar has completely lost its shell, drain the vinegar. Hold the egg up to a light. Notice the yolk is moving freely inside. Hold the egg 2 or 3 inches over a plate and drop it. Notice its bounce. You can now peel the 4 eggs labeled 3 through 6 (save the 6 eggs labeled 1-6). If the marker did not bleed through the eggshell, mark each one with its number as you peel them. Take note of the film attached to the shell that peels away from the egg. Try bouncing each one on the plate like you did with the egg from the vinegar. Which egg bounces best? How high can you drop the egg with out it breaking and how high does it bounce?

Step Four

For the final part of this experiment we need to slice through each of the 6 remaining eggs to look inside them. I have some photos showing how to best hold the knife and egg. Please be careful and remember, always find an adult helper when handling knives!
   
Once you have sliced each egg in half, look closely at the insides. Feel the white part and the yolk. Which eggs are firmest, which are softest. Have any started to turn grey? Go ahead and try a small bite of the whites. Which ones taste best to you? Which ones are moistest, driest, firmest and most tender?

What happened inside our bouncy eggs?

Most rubbers (rubber bands and bounce balls) and plastics (water bottles and action figures) are made of very long molecules commonly referred to as polymers. These polymers are very similar to the proteins in the eggs. When eggs are cooked the proteins tangle with each other to form a lattice or structure that holds the egg together. You noticed that the egg that only cooked for 5 minutes did not hold together very well and the egg that cooked for 30 minutes was very firm and bouncy. Scientists call this elasticity. Bounce balls, rubber bands and plastics are similar to the eggs because the more tangled the polymers are, the firmer or harder the rubber or plastic is. We can also learn how long is best to hard boil an egg. The whites and the yolks set or form a lattice at different internal temperatures. At higher internal temperatures, the lattice is so tight that water is squeezed out of the egg (right through the shell!). You should have noticed that the eggs cooked for 15 to 20 minutes were tender, moist and fully set. Any longer than this and the eggs were too firm and dry to taste good. Less than that and your egg salad sandwich would run away!

Still wondering what happened to the egg shell on the egg you soaked in vinegar? Vinegar is slightly acidic. The shell of an egg is calcium carbonate, slightly alkaline. When the two meet, the vinegar slowly dissolves the shell. The bubbles that hold the egg afloat are carbon dioxide (CO2), the rest of the shell is water soluble calcium acetate. The film you saw when you peeled the eggs is a sac that holds the egg white and yolk inside.