Cinnamon’s Science Surprise: A surface tension experiment

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My kids are 5 and 3 and love it when we do surface tension experiments because they get to help with the entire process, from the first pour to playing with the experiment.

They like that they can take ownership of their science experiment. With easy experiments like these, they can do all of the steps themselves, keeping them engaged for even longer.

This surface tension experiment explores the hydrophobic nature of ground cinnamon and the strong surface tension of water. When you dip a finger into the glass, it comes out dry!

It’s a little bit of science and a little bit of a magic trick. Time to amaze your child with surface tension!

How to make the Cinnamon Science Surprise experiment

Supplies you will need

For this experiment, you’ll need:

Ground cinnamon
Glass of water

Before you start

Place a towel under your glass to catch any potential spills during your experiment.

Instructions

Here is how to do this experiment with your child:

Step 1: Sprinkle a layer of cinnamon in the glass of water

Sprinkle enough cinnamon in the glass of water to add a thick layer of cinnamon. Be sure that the cinnamon covers a complete layer and it’s mostly level (notice mine isn’t totally level, but that’s okay).

A layer of cinnamon added to the glass of water

Step 2: Dip your finger into the glass

Dip one finger into the glass of water and cinnamon. When you dip your finger in, be sure not to swirl it around!

Even though the cinnamon layer is hydrophobic, it’s not perfect. If you swirl your finger around in the water, you’re essentially breaking through the protective layer of cinnamon. This allows water molecules to come into contact with your skin, causing your finger to get wet.

Think of it like a thin film. While it can protect a surface from water, it’s not indestructible. If you disturb the film, it can be breached, allowing water to penetrate. Similarly, the cinnamon layer can be disrupted by movement, allowing water molecules to reach your skin.

Dipping finger in straight through the cinnamon

Step 3: Pull out a dry finger!

Pull your finger out of the water and cinnamon without swirling your finger around in the water. Your finger will come out dry, with just some dry cinnamon powder left on your finger!

Cinnamon, in particular its essential oil cinnamaldehyde, is nonpolar. That means it doesn’t mix well with polar substances like water.

When you dip your finger into the glass, the cinnamon forms a protective layer around it. This layer, being hydrophobic, repels the water molecules, preventing them from coming into direct contact with your skin and getting your skin wet during the experiment.

So cool!

Dry finger with a layer of dry ground cinnamon

The STEM behind the Cinnamon Science Surprise experiment

This experiment teaches:

Surface tension
Hydrophobic barrier
Sensory activity

How it works

The water molecules are attracted to each other more strongly than they are to the cinnamon particles. This creates a “skin” or surface tension.

The cinnamon does not mix into the water but instead stays as a layer on the surface of the water. This is due to cinnamon’s hydrophobic tendency.

When you dip your finger into the water, the cinnamon particles form a barrier between your finger and the water. The surface tension of the water keeps the water molecules from contacting your finger directly. This is why your finger remains dry.

Surface tension

Surface tension is like a tight skin on top of the water. It happens because the water molecules like to cling to each other, but instead of having molecules all around like inside of the liquid, the molecules at the surface only have molecules next to and below it.

Those molecules at the surface therefore pull inwards, forming a thin sheet at the surface. That’s why water droplets are round and some bugs can walk on water!

The layer of cinnamon rests on top of the water. Since the surface tension of water is strong and the cinnamon is hydrophobic, we can dip our finger through the cinnamon layer and it will come out completely dry!

Hydrophobic barrier

Have you ever tried to add cinnamon to your coffee or tea, but it just clumps up instead of mixing into your beverage? Well, there’s a reason for that!

Cinnamon is hydrophobic, which means it does not mix in water.

What makes cinnamon hydrophobic? Its chemical composition!

Cinnamon contains the essential oil cinnamaldehyde, which gives cinnamon its distinct flavor and aroma. Since cinnamaldehyde is nonpolar, it does not mix well with polar substances like water.

Therefore, however hard you try, the cinnamon you add to your coffee won’t truly dissolve and mix with the coffee.

Sensory experimentation

This fun experiment is not only for science, it’s also a wonderful sensory experience for your child:

Visual Appeal: The cinnamon creates a visually appealing effect on the surface of the water, which is fun to observe.
Tactile Experience: When they dip their finger into the water, they’ll experience the tactile sensation of the cinnamon particles on their skin.
Surprise Element: The fact that their finger comes out dry is a surprising and engaging element that will pique their curiosity.