How to peel an uncooked egg

Demonstration Experiment on Video

How to peel an uncooked egg

Objective: Release of Carbon dioxide from Calcium carbonate

Peter Keusch

German version

Supermarket products:
hen's egg
vinegar essence (25 %)

Apparatus and glass wares:
beaker 250 mL
petri dish d = 9 cm
watch glass d = 7 cm
tea spoon
knife

Experimental procedure and results:

A raw egg is placed into a 250 mL beaker containing 140 mL of vinegar essence. Tiny bubbles immediately start to form on the surface of the eggshell. The beaker covered with a watch glass is placed into a refrigerator. Next day the egg is carefully scooped out of the vinegar using a spoon.

Video clip (Download RealPlayer .rm file)

Discussion and background:

When an egg is submerged in vinegar, the shell begins to dissolve. Calcium carbonate in the eggshell reacts with acetic acid to form carbon dioxide.

The reaction is

After 24 hours the eggshell will be gone and portions of it will be floating on the surface. The egg remains intact because of the thin membrane that is normally between the shell and the egg white. The water from the vinegar moves through the membrane into the egg because the membrane is semi-permeable. So the size of the egg will be slightly increased.

The egg white turns to a rubbery substance. The egg white is mostly a protein called an albumin. Proteins such as albumins are easily "denatured" by acidifying. Denatured proteins become opaque. The yolk of the egg holds up better to the vinegar attack. While there is a lot of protein in the yolk, there is also a lot of fat and other molecules that make it more difficult to denature.

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