Halloween Science Projects: Bubbling Spider Leg Potion

Halloween. It’s the time for witch costumes, pumpkin heads, and STEM activities.

You might not think that the last thing fits in the list, but it turns out, there are so many fun Halloween STEM activities that you can try leading up to the spookiest holiday. In this experiment, we’ve put a spooky twist on the classic lava lamp experiment by adding spider legs to the mix. Kids will love these crazy Halloween science projects!

Halloween science and STEM activities are one of our favorite ways to bring STEM and science into every holiday.

Don’t miss the complete list of Halloween science experiments!

We’ve always wanted to try making the classic alka seltzer lava lamp, but never had. We decided to give it a Halloween twist by adding “spider legs” to the mix.

Halloween Science Projects: Bubbling Spider Leg Potion

This Halloween science experiment is simple and requires no upfront time investment, which is great for busy parents and teachers! This project is one of our numerous Halloween science projects that would also be a fun way to keep kids busy at a Halloween party.

What you’ll need for the bubbling spider leg potion:

Alka seltzer tablets (the more the better, the kids loved dropping them in repeatedly)
Oil (we used rice oil given to me by Riceland at a conference I attended and it worked great!)
Food coloring (we used red)
Chocolate sprinkles (these are the spider legs)
Science beakers (we used this set)

First, fill your beakers about 2/3 of the way full with your rice oil. Add enough water to fill the bottom up about 2-3 inches, depending on the size of your containers.

Add food coloring to the oil and watch it descend through the oil into the water. The kids thought this was almost as interesting as the potion itself. It reminded me of our rainfall science experiment we did a few years ago.

Add about 1/8 of a cup of chocolate sprinkles per beaker.

Let everything settle and mix on its own. Don’t touch anything, it will all resolve on its own.

Once the water is completely separated from the oil, add your alka seltzer tablets to the water. We divided our tablets into four pieces and dropped in one piece at a time. The water bubbled up into the oil, and so did the spider legs. It was the perfect mix of science and spooky just like we were hoping.

The Science Behind The Spider Leg Potion Halloween Science Project

As you can tell when you set this up, water is heavier than oil. Intermolecular polarity keeps things separated (basically, oil and water molecules don’t like mixing). But when the alka seltzer tablet is added, it creates gas when it dissolves. When the gas rises, it takes some of the water (and spider legs) along with it. The blobs of water/gas reach the surface of the water and when the gas escapes, the water blob falls back to the bottom of the beaker.