Halloween Science: Awesome & Easy Exploding Pumpkins!

My favorite halloween science activity

This Post Includes Instructions And Freebies For My Favorite Halloween Science Activity, Where Students Get To “Carve” Pumpkins The Fun Way!

It’s that time of year again! Leaves are swirling, temperatures are dropping, and kids are getting hyped for sugar overload.

Meanwhile, your favorite science teachers are busting out what are undoubtedly some of the most enjoyable activities of the year!

If you’re feeling a little unimaginative this year and are looking for something new and exciting, I’ve got you covered.

I look forward to this Halloween science lesson all through the dreaded October teacher slump that we all know so well.

I hope it will get you feeling pumped as we head into the challenging holiday months ahead

Halloween Science: Exploding Pumpkins Lesson Description

Summary: Students will use a chemical reaction to pop out the pieces of their carved pumpkins! Watch this quick video from Steve Spangler to get the idea!

Time Required: At least two 45 minute class periods. I usually stretch it out for the whole week of Halloween if I have time!

Materials Needed:

- Pumpkins (medium to large size) – Look for grocery stores or pumpkin patches that sell by the pound to save $$! They are also pretty easy to grow if you have a large, sunny area.
- Calcium Carbide (CaC2) – If you are purchasing for the classroom, order from a chemical supplier like this one. Otherwise, you can get a small bottle for pretty cheap on Amazon, just make sure to read the safety & storage instructions!

Water
Plastic cups – 5 to 8 oz ideally. Walmart is cheapest, but here’s a link if you want to buy in bulk.
Lighter or Blow torch
Drill with 3/8 inch bit (optional)
Waste container – I just use an old bucket filled partially with water.
Personal Protective Equipment
Extra garbage cans for clean up
Fire extinguisher (just in case!)
Students Slides for Lab Report (preview below)
Peer Grading Rubric

Essential Question:

Which <insert variable of choice here> will optimize energy release for the exploding pumpkin reaction?

Learning Goals:

Students can design a controlled experiment & balance chemical equations.
Students will create a summary presentation representing their experiment and reactions.

Introducing the Activity

This reaction has been used for many years by chemistry teachers to teach about exothermic reactions and alkynes, but it came to my attention through Steve Spangler and Science Bob.

I love to hook students into this activity by showing this video from Jimmy Kimmel!

I’ve structured this lesson as an inquiry activity that requires students to design and carry out a controlled experiment.

Over the years, my classes have played around with several variables in order to create the “ideal” explosion.

To support students through the process, I created an interactive Google Slide presentation!

Each student or group creates a digital copy of these Slides in which they plan and record their experiment.

Here is a preview of the student slides:

You can download these FREE SLIDES by clicking the button below!

Included in the slides is a link to the peer grading rubric, which you can preview below!

I use this rubric to guide students through giving peer feedback on each others’ experimental design, as well as to simplify grading for me.

Win win!

Finally, I will also send you a teacher version of the slides when you submit your email in the form below! (Email is required so students can’t access the key from Google.)

This teacher version of slides includes a key for the pre-lab and student examples for the experiment design.

Exploding Pumpkins Safety

If fire, explosions, and chemicals make you a little nervous, please don’t give up on this activity!

I promise that you can manage this activity safely if you follow the precautions outlined below.

First, review the Safety Data Sheets for each of the chemicals involved in the reaction. I’ve linked those here for convenience:
Next, select a well-ventilated outdoor area in which to complete the activity.
Third, be prepared with all the necessary personal protective equipment!
- - For teacher:
    - - Safety Goggles
      - Gloves
      - Lab coat or apron
      - Extra-long Tongs – so you can pick up and dispose of flaming pumpkin chunks
  - For students:
    - - Safety Glasses
      - Gloves if students will be handling the chemical. (Check your district chemical hygiene plan for a list of approved chemicals. In my district CaC2 is on the “teacher only” list for handling, so my students do not touch it.)
      - Optional: Lab coats or aprons
Finally, be prepared with fire-extinguishing equipment. I always have a bucket of water and a fire extinguisher ready, just in case.

NOTE: The small scale of the reaction helps to minimize risks and make safety manageable. That said, if you are homeschooling, it might be best to select an alternative chemical reaction with less hazardous risks.

See the “Variations” section below for more ideas!

How to Set Up for Exploding Pumpkins

The prep for this activity is actually pretty minimal.

First, gather all the materials & prepare all the necessary safety equipment as outlined above.
Then, measure approximately 1 gram of CaC2 into a plastic cup. Make one cup for each pumpkin you plan to explode.
Next, measure approximately 20 mL of water in a second container. Students will pour the water into the CaC2 cup inside the pumpkin to start the reaction. To make it quicker, I just bring out a bucket of water with a cup that I have pre-marked with a fill line at 20 mL.
Use a drill or have students carve a small hole in the back of each pumpkin where you will ignite it after the gas builds up. The smaller the better, but it needs to be big enough to fit the lighter through it.
Finally, set up a little platform for the pumpkins. I use a small table covered with aluminum foil. This makes it easy to clean up and prevents my wooden table from getting burned.

Variables for Testing

Like everything in science, the reaction doesn’t always work perfectly, so I love to have students explore some variables!

Here are a few of the variables I like to discuss with students before they design their experiment:

Reactant concentration – How much water is ideal for 1 gram CaC2? I don’t allow them to change the CaC2 mass, but they can increase the water volume.
Pressure – Needs to build up enough pressure to pop, but not so long that the gas starts leaking out the cracks. How much time is ideal for gas build-up?
Size – Large pumpkins vs small pumpkins. What size of pumpkin give the best pop?
Seal – Gas escapes when not sealed well. Different cutting techniques, carving from top vs bottom, duct taping lid. What type of seal works best?
Other ideas – Temperature, humidity, different gourds (squash, watermelon, one year we even blew up an eggplant!)

Exploding the Pumpkins!

Connecting Halloween Science to Curricula

Possible applications for chemistry classrooms:

Chemical Reactions (combustion, exothermic)
Balancing Equations
Stoichiometry
Products & Reactants
Bonding (ionic, covalent, triple bonds)
Gas Laws
Conservation of Matter

Possible applications for general science classrooms:

Variables & Experimental Design
Chemical & Physical Changes
States of Matter
Conservation of Matter
Energy Transfer
Balancing Equations
Lab Safety

General & Cross-Curricular Applied student skills:

Inquiry
Critical thinking
Problem solving
Collaborative groups
Observing
Analyzing
Summarizing
Communication
Digital skills

Variations on this Halloween Science Activity

Using H2 instead of Acetylene

I’ve never tried it in the pumpkin, but I believe you could get similar results to this activity by generating H2 from sodium borohydride and water.

Here are some fun examples of hydrogen explosions:

Build a Calcium Carbide Cannon

Another fun idea is to build a calcium carbide cannon like the one in this video!

This could also be a great addition to my “Thanksgiving Science Activity: Potato Shooters” here!

How was it?

I would LOVE to hear your feedback for this lesson! How did it go? What other fun Halloween science lessons have you tried in your classroom? Please share in the comments!