AUSTIN, Texas - In today’s demonstration, we’ll be making a fog machine with a few simple supplies. You’ll also get to see a few phase changes firsthand!
Here’s what you’ll need:
- Dry Ice, available at many grocery stores
- Warm Water
- A plastic or metal container
- Thick gloves
- Eye protection
- Adult supervision
- Optional: paper towel soaked in soapy water
Before we get started, let’s talk about safety!
Adult supervision is highly recommended during this experiment.
Dry ice is frozen carbon dioxide gas. CO2 gas doesn’t freeze until it reaches -110° F. This substance is incredibly cold and handling it with bare hands will result in injury. Make sure you have a pair of thick gloves to handle the dry ice. You’ll also want goggles or safety glasses to protect your eyes.
Finally, make sure you’re doing this experiment in a large well-ventilated space or outdoors. A buildup of CO2 gas in a poorly-ventilated space can be hazardous.
Let’s get started!
First, pick up the dry ice with your gloved hands. Do you notice the fog coming off of the chunk of dry ice? The dry ice is currently undergoing a phase change known as sublimation. That’s when a substance goes from its solid form directly to a gas, bypassing the liquid phase altogether.
If you were to leave the dry ice out, a 5-10 pound block would completely sublimate away in about 24 hours.
Fill your plastic or metal container about halfway with warm water. Now drop your chunk of dry ice into the water. What do you see? You should notice a lot of fog coming out of the container now.
If you’re using a clear container, the dry ice looks like it’s boiling! The bubbles you’re seeing are filled with carbon dioxide gas as it sublimates off the dry ice. Once this cold carbon dioxide gas reaches the surface of the water, it immediately cools the air above the water’s surface. This rapid cooling causes the water vapor in the air to condense into suspended water droplets...fog!
So the fog is a combination of carbon dioxide gas and water droplets.
It’s immediately sinking for two reasons: the fog is cooler and denser than the surrounding air and carbon dioxide gas is denser than air. This fog will continue to pour out of the container until the dry ice disappears, likely for a few minutes.
The larger the block of dry ice, the longer you’ll see fog.
If you want to take this demonstration one step farther, have a bowl of soapy water nearby with a paper towel soaking inside. Wring the paper towel out gently and run it around the rim of the bowl containing the dry ice and water. Then, stretch the paper towel out and drag it across the top of the bowl.
This will result in a bubble that covers the top of the container.
This bubble will fill with our dry ice fog, resembling a crystal ball! This bubble will burst when it can’t hold any more fog. This is a great demonstration for Halloween if you want to add an extra spooky element to your jack-o-lantern or you’d like to shroud your front yard with a layer of fog.