Eggs-periment Part 1 – Naked Eggs

The kitchen is the BEST place to look for materials to investigate with your kids.  This past week, we’ve been “eggs-perimenting” with eggs.  The first part is to create a Naked Egg.  WHAT??  Did I say NAKED??  Yes I did!  And that was enough to get the giggles going in our kitchen.  So simple.  Two ingredients that I know you have at home.

Here’s what you need to get started:

  • Eggs (At least 2 in case they break.  We used 4)
  • Vinegar
  • Clear Jars/Cups

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First I gave raw eggs to the superheroes to touch and observe.  Since mine are young, I had to ask them “probing questions” such as:

  • What color is it?
  • Is it bumpy or smooth?
  • Is it hard or soft?
  • What shape is it?

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Then we carefully added the eggs to the clear jars.  One egg per jar.  Add enough vinegar to cover the egg completely.  The eggs might float and leave the top uncovered.  This is okay.  You will most likely need to change out the vinegar the next day and you can invert it then.

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The superheroes immediately noticed the bubbles on the egg shells.  We talked about what that might be.  They asked if there was baking soda on the outside of the egg since they know that vinegar and baking soda creates bubbles.  I told them it was similar to baking soda but not quite. For those of you with older superheroes, baking soda is Sodium Bicarbonate and egg shells are mostly composed of Calcium Carbonate, both of which are bases that react when mixed with an acid such as vinegar (Acetic Acid).

We let the eggs sit overnight in the jars and observed them in the morning.  We started to notice a few things:

  • the eggs looked bigger
  • the egg shells were disappearing
  • there were lots of bubbles on the outside of the egg
  • the eggs looked yellower
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After 1 day, the shell is partially dissolved

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The froth on top is from the dissolved shell.

We discussed what was going on and the superheroes offered their own explanations. We carefully drained the jars of the vinegar and added fresh vinegar to continue to dissolve the shells.  I also gently rubbed on the eggs to scrape some of the shell off (it turns into a powder like coating that you can easily rub off) just to hurry up the process.  The eggs are very delicate at this stage as the only thing holding it together is a thin membrane. You might have noticed this thin membrane coating the inside of an egg shell when you crack them.  We DID end up losing an egg while draining one of the jars.  You can see the membrane floating at the top.

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After 3 days soaking in vinegar, this is what we ended up with.  A naked egg!

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A naked egg vs. a regular raw egg

And of course, the superheroes completed their observation sheets.

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The Science behind the Experiment:

There are a couple of things to note in this experiment.

First, and most obvious, is the dissolution of the egg shells.  As stated above, about 95% of an egg shell is composed of calcium carbonate which is a base.  When an acid like vinegar, also known as Acetic Acid, is added, the two chemicals neutralize each other, thus leading to the disappearance of the shell.  The bubbles that you see are carbonate ions from the shell that turn into carbon dioxide in this acid-base reaction.

Second is the obvious change in size of the eggs.  Once the shell disappears, a permeable membrane remains.  Permeable means that some substances can penetrate (or diffuse into) the membrane, such as water.  This process is called osmosis, the diffusion of water.  Many secondary teachers use this experiment to demonstrate how the membranes inside of our cells work.  (More on this in Part 2 of the Eggs-periment).

Follow this link for more details about this experiment:

http://www.exploratorium.edu/cooking/eggs/activity-naked.html

 

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