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 burning piece of paper.
- Erlenmeyer Flask, 1 L, narrow mouth
- Egg, hard-boiled, shell removed
- Safety Goggles
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. Wear safety goggles and gloves.
- Place a hard-boiled egg in the mouth of the 1-L Erlenmeyer flask and show that the egg will not pass through the flask’s mouth. Remove the egg.
- Hold the paper with the tongs, light it, and place it in the flask.
- Immediately replace the egg on the flask’s mouth.
- 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.)
What is happening?
As the paper burns, the pressure of the air inside the flask increases. 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.