2nd day: Naked eggs

What is a naked egg?

How does a naked egg look like?

What is osmosis? And how does it work?

These questions and a few more have been aswered in the scientific workshop than I have prepared today.

A naked egg is a regular egg that has lost its shell and it's obtained by putting the egg inside a vessel with vinegar. The kids have been quite amazed by touching these shell-less eggs. However, before playing with the eggs they have wanted to know how the eggs had gotten this effect. Therefore, I have explained the chemical reaction between calcium carbonate and the acetic acid present in vinegar to them. To make them visualize better the reaction, I put different eggs different time periods, this is how I have obtained some eggs that have hardly lost their outter color and others with the shell completely dissolved.

 

In the following pictures I show the "stages" of this process:

1. As soon as the egg is immersed in vinegar the reaction starts. The bubbles are created due to the CO2 formation.
2. After a while this CO2 bubbles are going to form quite a thick white foam and the initial color of the egg (orangeish) will turn to white and the pigment is seen as a stain on the surface.
3. The shell remains only in the part that didn't react with vinegar. It was like this because the egg was rotten, and rotten eggs float.  
4.  The egg when its shell got completely dissolved. 

Once all these explanations over, I've done an apparently very simple question to the kids:

Why naked eggs are bigger than regular eggs? None of them, but one, has ventured to answer my question, however that bold kid has made it right, even if he didn't know what osmosis is. He has correctly assumed that the vinegar had somehow filled the egg.

In this way, I have taken advantage of it and I have explained what the osmosis is by drawing a picture similar to this one here. As the shell gets dissolved the solvent will from the are with a lesser concentration of solutes to the more concentrated side, in an attempt to make both sides have the same concentration. Once both sided have reached this point, we will say that this system is in equilibrium.

However, I haven't talked to the kids about this last term, and I have limited myself to explaining that the solvent, vinegar in this case, will go from the area with a lesser concentration of solutes to the area with a higher concentration of them. To make it easier I somehow explained to the children that a solute can be a molecule just like sugar and salt and that it's kind of invisible when mixed with water, but in this case by saying that all these solutes are the proteins inside the egg.