Osmosis

On Monday, the 4th grade finished the last stage of their osmosis experiment. They began the Growing and Shrinking Egg experiment by dissolving the egg shells in vinegar. The vinegar's acetic acid reacted with the calcium carbonate of the egg shell to produce carbon dioxide, calcium, and water. While you don't notice the water, and might not see the calcium, you definitely notice the bubbles of carbon dioxide gas form on the egg and release to the surface. The result is a shell-less egg with just the membrane left behind.

Once the eggs' shells vanished, the students started the growing and shrinking process with corn syrup and water. Corn syrup has a very high density that comes from a high concentration of dissolved sugar. These sugar molecules are too large to pass through the semipermeable membrane of the egg, but the water molecules from the egg can. These water molecules pass through the membrane of the egg into the corn syrup until the concentration of water molecules is the same on both sides. The water movement, from egg to syrup, results in the shrunken egg. The other eggs that were soaked in water grew, but why? Just as the concentration of water molecules is higher in the egg than in the corn syrup, the egg has less water concentration than that of the water. Water molecules are moving into the egg, instead of out. The increase in water results in the expansion of the egg!

Before saying goodbye to their eggs the students decided they had to give them a proper sendoff and made containers for their eggs to "travel" in. It was a fun and creative end to a very popular experiment!