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You may have heard of a self-carving pumpkin. The self-carving pumpkin uses a chemical reaction to cause an explosion inside a pumpkin, forcing out the pumpkin pieces of a jack-o-lantern face (with an accompanying bang and fire). You can perform this popular chemistry Halloween demonstration yourself:

Self-Carving Exploding Pumpkin Materials

  • 50 ml hydrogen peroxide (H2O2)
  • 20 ml water
  • ~7 pea-sized chips of calcium carbide (CaC2)
  • cat food or tuna can
  • oven mitt (to avoid getting burned)
  • piezoelectric sparker

Make a Self-Carving Pumpkin

  1. Carve a medium pumpkin with a simple face. Re-insert the face pieces, making sure they can move easily out of the pumpkin. If the pumpkin has thick flesh, you may wish to cut away the back of the pieces so they are lighter/weaker.

  2. Poke or drill a small hole in the back of the pumpkin so you can insert the wire sparker. Insert the sparker and test it to make sure it works.

  3. Pour the peroxide in the pumpkin. (an optional step in some descriptions)

  4. Put the water in the cat food or tuna can and set the can in the pumpkin.

  5. Drop the calcium carbide chips into the water and replace the lid of the pumpkin. Allow about a minute for the acetylene to build up.

  6. Be sure the face of the pumpkin is facing away from you and that your audience is a safe distance from the demonstration. You may wish to wear ear protection. Goggles and a lab coat are recommended. While holding down the lid of the pumpkin (with an oven-mitted hand), spark the sparker.

How the Self-Carving Pumpkin Works

In 1862 Friedrich Wöhler discovered calcium carbide and water would react to form flammable acetylene gas and calcium hydroxide (video of the reaction):

CaC2 + 2 H2O → C2H2 + Ca(OH)2

This reaction is used in the commercial manufacture of acetylene and for carbide lamps, which are used by miners in some areas.

Safety Precautions

This demonstration is best performed by a chemistry teacher or other adult experienced with chemicals or pyrotechnics. It is not a suitable project for kids to try. You'll likely need to order calcium carbide through a chemistry or educational supply store or else buy it online. Remote ignition of the acetylene is safer than holding the pumpkin and striking a sparker, though you'll want to secure the lid of the jack-o-lantern so that it won't simply blow off, leaving your pumpkin uncarved. If the pieces of the face are not loose, either the pumpkin will explode or else the explosion will be contained and the pumpkin will be uncarved.

If you have performed this demonstration and have additional tips or tricks or if you have further questions, please post a response.

Comments

October 6, 2010 at 12:40 pm
(1) Emily says:

I am thinking about doing this for a Chemical Engineering activity with High School students. Is there any way to combine this with the colored smoke pumpkin or would that be to much of a risk since your causing an explosion in the presence of methanol? Thanks so much.

Emily

October 14, 2010 at 10:46 am
(2) chemistry says:

I would not combine it with colored smoke, though you might add boric acid or borax to see if you would get green flame. The explosion is very quick, so I doubt colored smoke or flames would provide much of an additional effect.

October 13, 2010 at 8:07 pm
(3) Sandy says:

Questions:
Where does one get, ~7 pea-sized chips of calcium carbide (CaC2)
Purple smoke pumpking? where’s that one/

Never heard of this, and am dying to try it

Thanks !

October 14, 2010 at 10:44 am
(4) chemistry says:

You can order calcium carbide online at any scientific supply store or from a mining supply store. Just do an internet search for “buy calcium carbide”.

October 19, 2010 at 5:39 am
(5) Sandy says:

ATTENTION ALL !

I WAS QUITE EXCITED ABOUT DOING THIS, AND GOOGLED IT, AND FOUND OUT THAT IT IS VERY DANGEROUS.

YOU GET THE CA CARBIDE FROM THE MINING STORE ! EXPLOSIVES !

NOT FOR THE DO IT YOURSELFER AT HOME WITH THE KIDS.
DANGER OF TOXIC FUMES, SMOKE, FIRE.

WAS PERFORMED ON TV WITH A SUPPORTING FIRE CREW ON STANDBY.

SORRY, I WAS DISAPPOINTED TOO. BUT BETTER THAN HAVING A DISASTER.

? why was this in the weekly newsletter to the ordinary folks?

October 30, 2010 at 11:40 am
(6) Lynn says:

I did this for my chemistry class on Friday and undercut the CaC2 since this was my first time trying it. It worked! but without the huge sound and powerful push. So I’m doing it again with the suggested amount next week.

I love your demos Dr. Helmenstine! They are clearly explained with safety guild lines. And, you include the teaching materials. I have used many of your demos with fantastic results in the past.

Thank you for your newletters.

October 25, 2012 at 12:19 pm
(7) Bob Kahn says:

I have done this every year with my middle school students.

I test it out with a colleague first without kids. I also carve out two big simple ear pieces to relieve some of the pressure. I have kids wear safety goggles and plug their ears.

Question though- Sometimes it works for me, other times
I just get a puff of black soot and the inside of is covered with black soot.

Any ideas why this happens and how I can prevent it?

Also- I have never used the hydrogen peroxide- is this just directly poured into the pumpkin itself?

Thanks so much.

October 29, 2012 at 12:20 pm
(8) Stewart says:

the soot and puff of smoke with black soot everywhere is due to incomplete combustion.

You didn’t have enough oxygen for the combustion reaction, and the hydrogen peroxide is likely used as a source of extra oxygen gas since it naturally decomposes into water and oxygen gas.

Hope this helps.

October 31, 2012 at 9:44 pm
(9) Stewart says:

hERE’S WHERE YOU CAN BUY THE PEA-SIZED PIECES OF CALCIUM CARBIDE:

http://cheapcarbide.com/cc/index.php?main_page=index&cPath=66

November 4, 2012 at 9:04 pm
(10) One Eye Willie says:

I lost an eye doing this. Now I live in a barn in Cheryl’s backyard.

October 30, 2013 at 7:22 pm
(11) Bob K says:

I have done this many years and it works great. This year I do not have any calcium carbide. Could this work if you the pumpkin was filled with two parts hydrogen gas and 1 part oxygen gas? I have done this with balloons and it makes a big boom and fireball but I have never done it with a pumpkin. Thanks so much.

February 22, 2014 at 6:41 pm
(12) jusjac says:

I use this with my middle school students. It is great for demonstrating reaction. I drill a hole in the back of the pumpkin and use a long butane lighter. If you leave the crystals too long without lighting it, it will displace the oxygen needed for combustion.
I have also made a shield out of plexi glass much like the 300 used in their great skirmish.
Make sure the parts do not fit too tightly.
Lots of fun

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