Dry ice is a fascinating substance, and perhaps you have seen it filling the stage at a rock concert or viewed volcano experiments at a school science fair. But why exactly does dry ice, a solid substance, turn into cold, white vapor at room temperature? The answer lies in its chemical composition.
Dry ice is a compound consisting of one carbon dioxide molecule chemically bonded to two molecules of oxygen and not an element or a mixture. At room temperature in its solid-state, dry ice does not melt, but instead, it sublimates directly to a gaseous state and creates a thick vapor.
This article will examine compounds, elements, and mixtures in order to appreciate the chemical makeup of dry ice better. Following this review, I will discuss common sense and safety rules for the proper use, management, and storage of dry ice and even a fun experiment or two.
What are Compounds, Elements, and Mixtures?
Compounds are made of molecules that are composed of more than one chemical element bonded together. For example, water is a compound of Hydrogen to Oxygen in a 2:1 formula. A compound can be broken down into its constituent elements by chemical means only. Therefore, a molecule must consist of two or more elements.
Every compound hosts a chemical formula that articulates how many atoms of which element are in the compound. For example, dry ice is Carbon Dioxide, CO2. From 118 elements commonly identified, there are an astonishing 350,000 chemical compounds registered today.
Elements are singular atoms or groups of atoms that cannot be broken down further by physical or chemical means. They are groups of atoms with identical numbers of protons in their atomic nuclei.
Mixtures are groups of atoms that include elements and compounds that are not chemically bonded together and may be separated by non-chemical (physical) means. For example, consider oil and water, they are mixed together, but their internal properties remain the same.
(Source: Compounds, Elements, and Mixtures)
Dry Ice: Compound, Element, or Mixture?
Dry ice is a compound. Carbon dioxide (CO2) in solid form, one carbon atom joined with two oxygen atoms (1:2). These compounds may not be separated except by chemical means.
Dry ice is a pure substance (compound) that does not melt. It bypasses the liquid state and forms directly from solid to gas (sublimation), and contrariwise, from gas to solid (deposition). According to ASCO, at standard atmospheric pressure, dry ice has a temperature of approx. -79°C (-110,2°F).
What Is Dry Ice Used For?
Dry ice is mainly used for refrigeration of items that need to be kept very cold, like perishable food and medications. Anywhere there is no mechanical or cyclic cooling system.
Examples include inserts for large packages
or smaller inserts for your child’s lunchbox.
There are some lesser-known but no less interesting uses for dry ice you might not have thought of, courtesy of Iceman:
- Increase yield from plants
- Bed bug traps
- Chemotherapy caps
- Fresh meat processing
- Green burials
- Mosquito traps
Dry ice is not just for your kid’s volcano experiment anymore.
How Do You Make Dry Ice?
Global dry ice producer ASCO describes the process. Dry ice is produced from liquid carbon dioxide (CO2). Using what they call a dry ice pelletizer, the liquid CO2 is allowed to expand to form dry ice snow. Finally, the dry ice is pressed to form its suited purpose, be they tiny pellets (1.7 -3mm) for dry ice blasting or larger blocks for cooling needs.
When dry ice is exposed to room temperature air, a thick fog or vapor forms due to the extreme cold temperature. This vapor is composed of water droplets within the carbon dioxide gas molecules, which are then slowly released, forming a highly visible and chilly vapor or fog.
Why Should I Use Dry Ice?
Dry ice is used more often than you might think. The international ice company, the Iceman, notes its proliferance in the shipping industry, as it is easy to make and is the ideal temperature for sensitive shipping solutions for industries as diverse as medical laboratories, catering companies, and photographers.
Quint Marini, a shipping expert package engineering manager at UPS Package Design and Test Lab, notes that due to its extreme cold temperature (-109.3°F or -78.5°C), dry ice is often used for items that require extreme cold. Examples of this are frozen food and certain biological items. Additionally, dry ice is readily available, relatively low cost, and comes in various sizes.
How Do I Handle Dry Ice Safely?
Be extremely careful when handling dry ice. Given that sublimation occurs at -78°C (-109.3°F), it is extremely important that you do not touch it with bare hands. Luckily, there is no shortage of safety equipment for handling dry ice. Proper safety equipment for handling dry ice should include gloves, lab goggles, tongs, and a container to transport the dry ice.
For example, UPS has serious word protocols when it comes to dry ice as it moves through their supply chain. They note that any of their handlers that come into contact with dry ice must wear goggles, special gloves, and bibs to prevent any particles from getting underneath clothing.
Keep these rules in mind when handling dry ice:
- Hands-off and gloves on.
- Make sure you are in a well-ventilated space to avoid inhaling the vapor.
- Adult supervision is a must.
- Keep it away from pets.
- Do not keep in a closed container. The sublimation process will intensify air pressure, and the container will explode.
The Science of Dry Ice: Experiment Time
How can I learn more about dry ice? Hands-on (well, technically off) science experiments, of course. Here are some ideas:
- Halloween Fog: Hot water mixed with dry ice will blanket your space with a thick, creepy fog. Ratio: 1lb (0.53 kg dry ice to 1 quart (4L) of hot water. Use a pound of dry ice for every 4L of hot water for 5-10 minutes of maximum effect.
- School Science Fair: Here are links to YouTube videos for using dry ice in the following science experiments: volcanoes, comets, and cloud chambers.
Dry ice is a chemical compound, as opposed to an element or a mixture. Both functional coolant replacement for lack of functionality and fun, dry ice is nevertheless a dangerous chemical and should be approached with caution and proper safety protocols.
Incidentally, if you are thinking about getting that super-creepy Halloween fog effect, I would recommend Freezin Fog Juice for your dry ice and Amazon’s Choice ADG Fog Machine. The Fog Juice not only has a long dwelling time but is great for most fog machines. The ADJ machine is a natural complement to the Juice.
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