Thursday, March 24, 2011


Over the past two weeks we conducted an experiment into the permeability of an egg's shell and membrane.

The first step was to cover a raw egg with vinegar.  An egg's shell is composed of calcium carbonate (limestone) which immediately reacts with vinegar to produce carbon dioxide--that's all the little bubbles (gas) on the egg:

Day 2

Day 3

Day 5

The vinegar completely dissolved the egg's shell, but not its membrane.  The egg also increased in size because because of osmosis.  "Water always moves through a membrane in the direction where there are more dissolved materials, so the water in the vinegar moves through the thin membrane into the egg because the water inside the egg has more materials dissolved in it than does the vinegar" (Janice VanCleave's "201 Awesome, Magical, Bizarre, & Incredible Experiments." 35)

Next, we submerged the egg in corn syrup.

Day 2

Day 5

From The Science of Cooking: 
After you dissolve the eggshell, the egg is surrounded by a membrane. (Actually, it’s two membranes, but they are held tightly together.) This membrane is selectively permeable—which means it lets some molecules move through it and blocks other molecules.
Water moves through the membrane easily. Bigger molecules—like the sugar molecules in the corn syrup—don’t pass through the membrane.
When you put a naked egg in corn syrup, you are creating a situation where the egg membrane separates two solutions with different concentrations of water. The egg white is about 90% water; corn syrup is about 25% water. In this situation, random movements of water molecules cause them to move from the side of the membrane where they are more abundant to the side where they are less abundant. So water migrates from inside the egg to outside the egg, leaving the egg limp and flabby
Now, we're going to soak the egg in water and food coloring. Stay tuned......

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