Rubber Egg

Angel Lee Gilbert Douglass Middle Academy
543 N. Waller
Chicago IL 60644
(312) 534-6176


To demonstrate the semi-permeability of a cell membrane
To lay ground-work for discussion of osteoporosis

Materials Needed:

1 raw egg in its shell clear vinegar
1 jar with a lid flexible tape
(egg must fit inside the jar)


1. Measure and record the circumference around the center of the egg.
2. Record the appearance of the egg.
3. Place the egg inside the jar. DO NOT crack the shell.
4. Cover the egg with vinegar.
5. Close the lid.
6. Observe immediately, and then periodically for the next 72 hours.
7. Remove the egg after 72 hours and measure its circumference.
8. Compare the appearance of the egg before and after being in the


The egg has a hard shell on the outside and the circumference will vary.
Bubbles start forming on the surface of the egg's shell immediately and increase
in number with time. After 72 hours, the shell will be gone and portions of it
may be seen floating on the surface of the vinegar. The egg remains intact
because of the thin see-through membrane. The size of the egg has increased.
The shell of the egg is made of calcium carbonate, commonly called
limestone. When vinegar chemically reacts with the limestone, one of the
products is carbon dioxide gas, those bubbles seen on the egg. The membrane
around the egg does not dissolve in vinegar, but becomes more rubbery. The
increased size is due to osmosis, the movement of water through a cell membrane.
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. Water will always move through a membrane in the direction where there
are more dissolved materials. The contents of the egg stayed inside the
membrane because the molecules were too large to pass through the tiny homes.
This selectiveness of materials moving through the membrane is called semi-

Performance Assessment:

This is a pass/fail activity.

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