The chemistry demonstration called the self-carving pumpkin¹ is a blast (no pun intended) to conduct around Halloween. To prepare this experiment, a jack-o-lantern face is carved into a pumpkin, but the eye, nose, and mouth pieces are saved. These pieces are then gently placed back into the holes in the pumpkin. Next, a small hole (through which a nozzle-nose lighter can be inserted) is cut in the back of the pumpkin. When ready to carry out the experiment, calcium carbide is added to a container of water positioned in the jack-o-lantern, and the “lid” is placed on top. Acetylene gas builds up inside the pumpkin from the reaction between the calcium carbide and water:

CaC₂(s) + 2 H₂O(l) → Ca(OH)₂(s) + H₂C₂(g)           Equation 1

After a few seconds of allowing the acetylene gas to build up inside the pumpkin, it is ignited with the lighter:

2 H₂C₂(g) + 5 O₂(g) → 4 CO₂(g) + 2 H₂O(g)           Equation 2

The acetylene combustion causes the face pieces to shoot the pieces out of the pumpkin, and simultaneously ignites burning flames inside!

This experiment is so much fun that I just had to figure out how to modify it so I could conduct it at other times during the year (Video 1). By the way, Karen Sorenson (@sorensensci) taught me how to conduct this experiment using an entire line of pumpkins, such as what you see in the beginning of Video 1. If you try this experiment, be sure to use ear protection in addition to the other necessary precautions.

I think I know what experiment I’ll be doing around July 4th this year…

Reference:

1. https://www.flinnsci.com/api/library/Download/5366ba7521024667929f641dc2904d57