The Self-Carving Pumpkin: It's Not Just for Halloween!

exploding watermelon with carved face

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…




Safety: Video Demonstration

Demonstration videos presented here are not meant as tools to teach chemical demonstration techniques. They are meant as a tool for classroom use. The demonstrations may present safety hazards or show phenomena that are difficult for an entire class to observe in a live demonstration.

Those performing the demonstrations shown in this video have been trained and adhere to best safety practices.

Anyone thinking about performing a chemistry demonstration should first read and then adhere to the ACS Safety Guidelines for Chemical Demonstrations (2016) These guidelines are also available at ChemEd X.

General Safety

For Laboratory Work: Please refer to the ACS Guidelines for Chemical Laboratory Safety in Secondary Schools (2016).  

For Demonstrations: Please refer to the ACS Division of Chemical Education Safety Guidelines for Chemical Demonstrations.

Other Safety resources

RAMP: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies


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Comments 2

Elena Tchesnokova | Wed, 06/07/2023 - 15:41

Hi Tom,

Could you please advise what the safe amount (grams) of CaC2 is for the indoor demonstration? I am going to use small watermelon.

Thank you,


Tom Kuntzleman's picture
Tom Kuntzleman | Thu, 06/08/2023 - 16:14

Hi Elena:

This is difficult to answer, as it depends on how "fresh" your calcium carbide is. I would recommend first trying the experiment with no more than 0.5-1.0 g in 100 ml of water and scale up from there if need be.