We see diverse use of dry ice around us (with some special handling, of course!). It’s one of the coolest substances which Charles Thilorier, a French chemist, first observed. When he opened a liquid carbon dioxide container, he noticed the chunk of ice evaporate instead of melting. Its usage has surely expanded ever since.
Dry ice is basically carbon dioxide in its solid-state. Due to its sublimable qualities and high melting point, it is used in shipping preserved items with low melting points such as meat, chocolates, ice-creams, etc.
So, does dry ice melt? Dry ice does not melt at normal atmospheric pressure but undergo sublimation. Below -79 degrees Celsius and under 1 atmospheric pressure, it tends to transform into carbon dioxide gas. This is because carbon dioxide (CO2) can only exist in two states: solid and gas.
To turn it into a liquid, it needs to be combined with another element resulting in a change in its chemical formula. Therefore, carbon combined with only oxygen to form carbon dioxide is stable in its solid and gaseous state.
However, liquefied carbon dioxide is extracted from ammonia and hydrogen plants. But these also contain other compounds and can only be used for commercial purposes and not for laboratory experiments.
Why Does Dry Ice Not Melt?
The melting properties of dry ice can easily be understood by understanding the term sublimation. To change the state of a compound, we need a particular temperature and pressure at the same time. The natural pressure present in our environment is equivalent to 1 atmosphere.
It is interesting to note that carbon dioxide in normal atmospheric pressure of 1atm can only be stable in its gaseous and solid form. When it comes to liquid form, you need to combine it with another compound or increase the pressure.
Therefore, if you want to create liquid carbon dioxide, it is only possible in laboratories.
The above carbon dioxide phase diagram shows that as the steepness of the slope rises, so does the likelihood of carbon dioxide melting. This is because a steeper slope increases pressure while maintaining the same temperature of -78 degrees Celsius.
This exact condition is favorable for solid carbon dioxide or dry ice to melt.
This state is only possible in laboratories inside pressure cans. To melt dry ice in its liquid form, you would be required to exert 5atmospheric pressure at -78 degrees Celsius.
How to Avoid Sublimation in Dry Ice?
Sublimation can be caused by the presence of heat. So, in the first place, you need to keep the dry ice away from heat.
How to do that?
An estimated amount of 5lbs is sublimated from dry ice within 24 hours. Unfortunately, you cannot stop it from sublimating, but you can definitely slow down the process.
Tips to Handle Dry Ice
Below are a few tips you can follow while handling dry ice:
1. You must preserve dry ice in an insulated container to avoid easy sublimation. The best option is a polystyrene box.
This is also commonly known as a cooler. It is cold from the inside, and therefore it stops the dry ice temperature from going up, which in return forbids sublimation.
2. Always use rubber gloves to handle dry ice. When you touch dry ice, due to conduction, its temperature can increase.
However, rubber gloves do not promote conduction, and the temperature of the dry ice can remain intact, or there can be little changes. Rubber gloves also prevent your skin from ice burning.
3. Do not open the seal until you need it. When it is shipped, it is protected with various insulating layers to avoid sublimation.
So, we suggest you not open the seal if you want to increase the shelf-life.
Why is Dry Ice More Preferred Than Normal Ice?
The very property of dry ice to sublime instead of melting makes it a suitable fit in various instances.
1. Dry ice does not melt– when regular ice starts melting, it can leave patches of water, which can look messy and even spoil the packaging and the product.
In such cases, dry ice is used as it is neater, and even if it sublimes, it does not leave any patch on the product. Instead, it simply evaporates and vanishes from the spot. Due to this property, dry ice is widely used for refrigeration during traveling.
2. Another primary reason why dry ice is preferred for deep storage is because of its extremely low temperature.
Ice can keep a product cool, but dry ice helps in freezing the product. Freezing is a good method of preserving, and thus dry ice is used to preserve products like meat, ice-creams, confectionaries, etc., for long-distance shipping.
3. The rate of melting for dry ice is also slow as compared to regular ice. Therefore, you can preserve your product for a longer period without damaging it.
Possible Hazards Due to Dry Ice
Dry ice can act both as a friend and foe if not handled with care. However, before handling it, you must educate yourself about its properties and chemical reactions.
1. Do not handle dry ice with bare hands. Always make sure to wear gloves before holding them. This is because the temperature of dry ice is very low (below -78 degrees Celsius), and it can cause frostbite on your skin.
2. Dry ice is basically solidified carbon dioxide. Carbon dioxide is present in our atmosphere, but its proportion is very low (0.4%), consumed by plants. However, if you get stuck with dry ice in a room with no ventilation, there is a chance that you might get suffocated.
Gradually the dry ice would start sublimating, and the CO2 would not escape due to lack of ventilation. When you inhale CO2 instead of O2 for long, your blood vessels will carry CO2 in your body parts, and it can result in distorted functioning.
Eventually, you will suffocate and die. This is a significant disadvantage with dry ice. Therefore, it is essential to work with it in a well-ventilated space. Do not store it in enclosed areas like cars, closets, compartments, walk-in coolers, freezers, etc.
3. Do not store it in air-tight containers like a glass box. This can cause an explosion due to the accumulation of carbon dioxide with time.
Take special precautions during the disposal of dry ice. Do not dispose of it in your sink, toilet, bathtub, or any other drain of your locality. It can affect your drainage system because of the temperature variation.
Also, do not use garbage bins to dispose of it. If you want to dispose of it, let it sublime naturally. Make sure to sublime it only in an open space.
How To Understand Sublimation of Dry Ice?
The easiest way to understand the sublimation of dry ice is the dry ice-water experiment.
In this experiment, you need to put a piece of dry ice into warm water. Warm water will change the temperature of the dry ice, and it will start to sublime. Soon, bubbles would start forming near the ice. This bubble contains no water.
As a result, water will evaporate and go inside the CO2 bubbles. Due to the low temperature of CO2 bubbles, water would condense into tiny droplets.
This equation will follow Le Chatelier’s principle. And thus, their droplets would take the shape of a cloud. With the visible cloud, the process of sublimation is dry ice can be observed clearly.
Dry ice is a very interesting compound to play with. Along with the properties of Co2, many fun experiments are possible with dry ice.
From the above article, now you must have got the idea about how to melt a piece of dry ice and if it is possible under atmospheric pressure. But, unfortunately, liquid carbon dioxide is not purely used in commercial products, and even if it is used, they only utilize it to make dry ice out of it.
Always have your lab instructor with you while handling dry ice since it can cause severe health hazards if not handled well.
Follow all the instructions before performing any experiments with it, especially if you wish to melt it into liquid. The glass beaker has a chance to explode if handled casually. Thus, take necessary actions.