The frozen and compressed form of carbon dioxide is known as Dry Ice. If carbon dioxide is stored at 300 psi pressure, then it turns into a liquid. When filled in a container, the liquid turns into a white powder which is pressed together to form the solid dry ice. At normal pressure, it evaporates directly into the gaseous form and does not melt to form water. This process is known as sublimation.
When you pickup dry ice from the store, ensure that the windows of the car are down on the way back home. Further, due to the extremely low temperature, it can cause skin damage. Hence, tongs or insulated gloves must be worn. Goggles too must be used when crushing it to ensure that it does not enter the eyes.
Let us get on with the experiments now.
Inflating the Balloon
This experiment is a lot of fun, especially if you have a swimming pool close by. Take an un-inflated balloon and force the neck to open wide with the help of the middle and index fingers of both the hands. Ask someone to carefully drop in a few pieces of dry ice ensuring that it does not touch your fingers. Tie the balloon tightly and drop the balloon in a swimming pool. If you do not have a swimming pool close by, you can set the balloon aside or even drop it in a bucket, but the effects will not be as dramatic. When the balloon is dropped in the swimming pool, it will sink. However, as the pieces begin to sublimate, the balloon will slowly be filled with carbon dioxide and will start rising to the surface where it will float. If the quantity of the dry ice that was put into the balloon is excessive, then it may even explode.
Making a Spoon Sing
This is a very interesting experiment which you can use to teach students the concept of sublimation and pressure. To begin, warm a spoon by holding it above a flame for a few minutes. Now, place the spoon firmly against the chunk of dry ice. As soon as the warm spoon touches the dry ice, it sublimates and carbon dioxide is produced which tries to escape but the spoon will try to prevent this from happening. In this process, when the spoon is pressed against dry ice, it is forced away slightly because of the large amount of gas that is produced. However, because of the pressure that you are applying on the spoon, the spoon will fall back. This vibration of the spoon causes a loud singing like sound which people standing around the table can distinctly hear.
Smoking Water Fountain
This experiment can produce good visual effects. If you do not have access to a small water fountain, you can use a small bucket or tub to produce the same effect. However, you have to ensure that the water is warm. So, if you are using a water fountain, you can carry out this experiment on a warm summer day when the water in the fountain is tepid, else you will need a bucket or a tub. To begin the experiment, you need to first pound the dry ice into small pieces. To do so, place the it into a plastic packet and tie the packet up firmly. Now pound the packet with the help of a hammer. Once it has broken down into small pieces, scatter a few pieces in the warm water. You will immediately see white smoke rising from the water. This is nothing but condensed carbon dioxide. The quantity of smoke will depend on how hot the water is and also on the quantity of dry ice put in the water.
This experiment can also be used to teach young students the difference between alkaline and acidic liquids. In a glass containing water and ammonia, add some universal indicator solution. The liquid in the glass will turn blue. Now add some pieces of dry ice. It will be seen that the solution gradually turns red. Next, add some more ammonia to the container. The liquid will turn blue again. This is because ammonia is alkaline in nature while dry ice combines with water to produce an acidic solution.
I hope that you have found the experiments listed above useful and will enjoy using them to teach your children and students the properties of dry ice and a few concepts of chemistry.