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Egg Vacuum Activity

Genetic witness

If you are looking for an attention-getting demonstration of the gas laws for physical science students at any grade level, this is it. Basic equipment includes a hard-boiled egg, an Erlenmeyer flask, and an alcohol-saturated cotton ball. You can vary the demonstration by using different-sized flasks and soft-boiled eggs. This one is lots of fun for teacher and student alike.

Important safety note: This demonstration uses ethanol, which burns with a nearly invisible blue flame. Use caution.

Important safety note: Always check glassware for cracks or air bubbles before use. Never use any glassware with cracks or air bubbles in it for this or any other demonstration.

Materials needed

  • Ethanol, 95%
  • Tongs
  • Beaker, 50 mL
  • Erlenmeyer Flask, one L, narrow mouth
  • Erlenmeyer Flask, 500 mL, narrow mouth
  • Erlenmeyer Flask, 2 L, narrow mouth
  • Two hard-boiled, extra large eggs, shell removed (One each for Parts A and C)
  • One extra large egg, soft, shell removed (For Part B)
  • Cotton Balls
  • Lighter
  • Waste Bottle
  • Safety Goggles
  • Gloves

Preparation

For Parts A and C

Boil 2 eggs in water for 10 to 15 min. You will use one egg for Part A and the other for Part C.

For Part B

Two days before the demo, remove the shell from one egg with vinegar. Here is how to do it.

  1. Submerge the egg in a beaker of vinegar using the round side of a lab scoop.
  2. Replace the vinegar with fresh vinegar after 2 to 3 hr for best results. (The entire process requires about 2 days to complete.)

Demonstration

Part A: Traditional method

  1. Put on the gloves and goggles.
  2. Place a hard-boiled egg in the mouth of the one-L Erlenmeyer flask and show that the egg will not pass through the flask's mouth. Remove the egg.
  3. Grab a cotton ball with the tongs, saturate it with ethanol, light it, and place it in the flask.
  4. Immediately replace the egg on the flask's mouth.
  5. When the flame extinguishes, the egg is forced into the flask. (Note: If the egg does not get forced into the flask, repeat steps 3 and 4. The flame may go out before the egg is in place.)

Part B: Soft egg

  1. Put on the gloves and goggles.
  2. Place the specially prepared egg in the mouth of the 500-mL Erlenmeyer flask and show that the egg will not pass through the flask's mouth. Remove the egg.
  3. Grab a cotton ball with the tongs, saturate it with ethanol, light it, and place it in the flask.
  4. Immediately replace the egg on the flask's mouth.
  5. When the flame extinguishes, the egg is forced into the flask and bursts. (Note: If the egg does not get forced into the flask, repeat steps 3 and 4. The flame may go out before the egg is in place.)

Part C: Hard egg

  1. Put on the gloves and goggles.
  2. Place a hard-boiled egg in the mouth of the 2-L Erlenmeyer flask and show that the egg will not pass through the flask's mouth. Remove the egg.
  3. Grab a cotton ball with the tongs, saturate it with ethanol, light it, and place it in the flask.
  4. Immediately replace the egg on the flask's mouth.
  5. When the flame extinguishes, the vacuum rips the egg apart. Part of the egg is forced into the flask while the rest remains on the flask's mouth. (Note: If the egg does not get ripped apart, repeat steps 3 and 4. The flame may go out before the egg is in place.)

Disposal

Pour any ethanol residue into your liquid waste bottle. Discard the eggs in the trash.

What is happening?

As the cotton ball burns, the pressure of the air inside the flask increases (the egg actually bounces on the flask's mouth). When the oxygen in the flask is consumed, the flame extinguishes, and the air inside the flask cools. The resulting decrease in pressure creates a partial vacuum in the flask, which either forces the egg into the flask or rips it apart.

Make sure your students understand that it is not a decrease in air volume that creates a partial vacuum in the flask (the volume of the flask and the gases within remain constant). The partial vacuum in the flask is created by the decrease in air pressure caused by the rapid drop in temperature when the flame extinguishes.

Eggs-tension activities

  • Measure the pressure change using probeware.
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