The world of physics is a fascinating place filled with phenomena. Case in point — you can put an ice cube into a glass of water and watch it float peacefully. However, does dry ice (carbon dioxide in its solid form) float or sink in water?
Dry ice doesn’t float because it has a greater density than water. However, if dry ice pieces are small enough, they may rise to the surface and float due to the buoyancy of the CO₂ gas produced when dry ice comes in contact with water.
This article will explain what dry ice is and the physical properties that define buoyancy. I’ll also go over a few fun, safe ways you can use dry ice for home experiments or entertainment. Let’s get started!
Why Does Dry Ice Sink?
Dry ice sinks because it’s denser than water. However, as dry ice evaporates, the resulting CO₂ gas rises. This gas can cause smaller chunks of dry ice to float despite the difference in density.
A handful of physical properties of matter come into play when determining the buoyancy of an object. However, density, buoyancy, and Archimedes’ principle are the most relevant.
Density
Strictly speaking, the density of matter is the ratio of its mass to its volume. In other words, it’s how much stuff is occupying the space.
Here’s an analogy:
Think of it in terms of town population. Two towns of the same size are home to a different number of people. Town A has 20,000 people that live there, but Town B only has a population of 12,000 in the same size space. Therefore, Town A is denser than Town B.
Buoyancy and Archimedes’ Principle
Buoyancy, or up-thrust, is essentially the resisting force of a liquid that pushes back on an object’s weight. This force has a strength that is proportional to the difference in pressure. For example, how deep an object is submerged determines the amount of force the liquid exerts upon it.
We can further explain this in terms of weight and displacement, as described by the Greek philosopher Archimedes. His principle states:
“The buoyant force acting on an object submerged in water is equal to the weight of the liquid the object displaces.”
Think of it like jumping into a pool. When you submerge your body into the water, you displace the water to occupy the pool. As you splash into the surface, water gets pushed in all directions.
The water’s weight surrounding you is the acting force working against you, creating buoyancy.
To Float or Not to Float
When an object has a greater density than the liquid into which it’s submerged, it sinks. However, when the object is less dense than the liquid, the liquid’s buoyant force will cause the object to float.
Dry ice has a density between 1.2–1.6 g/cm³ (10.01–13.35 lbs/gal). We’ll use water as an example of a liquid, which has a density of 1 g/cm³ (8.34 lbs/gal). Dry ice is denser than water, so it won’t float but rather sink when submerged.
However, when dry ice comes in contact with water, it triggers desublimation — the solid ice transitions to a gas. This reaction causes bubbling in the water as the CO₂ escapes.
That’s because CO₂ is gas unless it’s under extreme pressure. The gas is less dense than water. So it’ll rise to the top and eventually disperse into the air beyond the water.
With that in mind, consider a tiny piece of dry ice as Batman, the buoyancy of CO₂ gas as his grappling hook, and the water’s surface tension surrounding the CO₂ bubbles as a high-rise in Gotham City.
Batman, our dry ice, is small enough that the grappling hook (CO₂) carries him up the high-rise, the tension holding the gas bubbles. Batman will appear to float, even though he is actually being pulled.
So even though dry ice will sink in water, a small piece can be carried by alternate forces and get suspended in the water, appearing to float. At the surface, then, there will be more fun physics to be observed, as the expelling of CO₂ will make tiny pieces of dry ice appear to dance and hover around the water’s surface, as though it were wearing a jetpack.
What Is Dry Ice?
Dry ice is the solid, frozen form of carbon dioxide (CO₂). Its creation begins with the compression of liquid carbon dioxide contained under pressure, for example, a fire extinguisher. When CO₂ is released and allowed to expand, some liquid vaporizes, and the rest freezes into solid dry ice.
This extreme cold caused by evaporation and change in pressure causes “snow” to form. This “snow” can be pressed into blocks, slats, or pellets that we call dry ice.
How Dry Ice Was Discovered
The first published account of observing frozen carbon dioxide was by Adrien-Jean-Pierre Thilorier. He made the discovery in 1835 while experimenting with the cast-iron tanks he invented for compressing gasses.
His tank had been filled with liquid carbon dioxide. Most of the liquid quickly evaporated when he opened the pressure valve, leaving behind dry ice.
Why Is It Called “Dry”?
We call it dry ice because liquid carbon dioxide doesn’t freeze into its solid form or melt into liquid.
When you hear ice, you usually think of wet ice made of water, where the phase transition goes from a liquid into a solid.
On the other hand, dry ice results from the change of a gas into a solid. This transition is known as sublimation. Conversely, the change from a solid into gas is known as desublimation or deposition.
Dry Ice Is Used for Chilling Goods
The temperature of dry ice is measured at -109.3°F (-78.5°C), making it very useful for cooling stuff. It’s more efficient and less messy than regular ice. Food and other perishable items, computer components, and biological samples are just a few examples of dry ice’s various industrial uses.
How Dry Ice Is Made
Reading the scientific explanation of dry ice is one thing, seeing it is another.
This short video gives a brief demonstration of creating dry ice using a fire extinguisher: https://www.youtube.com/watch?v=tLNHDxd6nDc
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First, the sublimation creates the “snow.” The “snow” gets captured and compressed in the drawstring bag and is ready to use.
Fun Home Experiments with Dry Ice
Whether you purchase dry ice or make it at home using a fire extinguisher, you can use it in various ways. For example, you can keep your refrigerator cold if the power goes out. But less practical applications are much more fun! This video shows fun experiments using dry ice you can try at home:
https://www.youtube.com/watch?v=MOgUpI4c2yk
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Using Dry Ice for Entertainment
A common application of dry ice is to make a thick, flowing fog to create a spooky Halloween ambiance. This is done by pouring hot water into a bucket of dry ice and using a fan to gently push and disperse the fog around the designated area.
Another fun and entertaining application of dry ice is putting it into beverages for a cool smoking drink effect. There are several recipes available online. You can search for inspiration to use at your next party. Just be sure to provide your guests with a nice swizzle stick, such as the Icicle Swizzle Sticks for Smokey Drinks (Amazon.com), to keep guests safe and entertained.
Icicle 50-Pack Drink Stirrer Swizzle Sticks for Smokey Drinks (Use with Dry Ice)
Dry Ice Safety Concerns
When handling dry ice, you must exercise caution and use protective equipment, such as insulated gloves. Its sub-zero temperature can cause frostbite.
Furthermore, while CO₂ is not toxic, oxygen levels in the affected area will gradually drop. This can cause difficulty in breathing, or hypercapnia, which is defined by increased levels of CO₂ in the blood.
Conclusion
Dry ice is the solid form of carbon dioxide created from its gas state through a sublimation transition. The density of dry ice is less than that of water, meaning dry ice doesn’t float when submerged in water. Instead, it sinks.
Dry ice is very useful and has many applications in various industries and entertainment.
Jake is a freelance writer from Pennsylvania who enjoys writing about science and sports. When he’s not writing for Temperature Master, he can be found watching the NFL or playing basketball with his friends.