This experiment would be best for students that are in 4th-8th grade as it seems to correlate best with the introduction of reactions and energy. Students will learn about different phase changes molecules can undergo. They will also learn about the bond strengths of substances and the ability to change the activity of a molecule using temperature.
Science Discipline(s)
Chemistry, Physical Science
Topics
Phase changes, Chemical bonds, Chemical reactions, thermal energy.
Activity Title
Witches cauldron
Materials
- Gallon or so of water (can also use punch or soda)
- Dry ice, broken into pieces or as chips
- Some type of viewing container like a pitcher or cauldron
- Protective work gloves
Procedure
- Add liquid to container
- Using protective gloves, add dry ice so that the liquid starts letting of a white layer of smoke
- Liquid can be added afterwards so that the mix continues to smoke. If you use punch or a soft drink mix, make sure that you remove any pieces of ice or dry ice before giving it to the kids. If a piece of dry ice were placed in a child’s mouth or they swallowed it, the dry ice could cause frostbite on areas contacted.
Questions
- What factors do you think are important in how much smoke is being given off in this activity? How could you design an experiment to test those variables for their effect?
- Would changing the temperature of the water make more smoke?
- How does the carbon dioxide stay in the soda?
- What happens when you shake a can of soda?
- Why does soda fizz when you open and why does it lose its fizz?
Explanation
During this experiment, we mix dry ice with water (or soda/punch) and see this awesome bubbly/smoke come from the ice. Dry ice is the solid (frozen) form of carbon dioxide. When carbon dioxide is in its natural state, it is a gas. When we freeze it, we slow down the atoms in the molecule and force them to stop moving around. When carbon dioxide encounters anything that is warmer than itself, it undergoes a phase change known as sublimation. Sublimation is the ability of a substance to go from a solid to a gas without first becoming a liquid. This means it will go from a block of dry ice to either gas or smoke. This process takes a while to happen and continues to happen for a while because of the bonds that make up water and the activity of the carbon dioxide atoms.
You could create more smoke faster if you added warmer water, but you would decrease the time it ran for. Just like with an ice cube, you can let it sit in a cup of cold water for a while and it will eventually melt. If you added it to warm water instead, it would melt much faster. Dry ice acts just like an ice cube, it can sublime faster or slower based on the temperature of the solution it is in. The cloud of smoke results from carbon dioxide gas escaping with water vapor. Since the gas is cold from the low temperature of the dry ice, the water vapor in the gas is condensed to water droplets that appear like a cloud.
Carbon dioxide is a stable molecule that can dissolve in water. It’s non-polar, meaning it doesn’t mix dissolve that well, however, with in water and the two parts will not react with one another in the can unless the water is pretty cold. As discussed before, at colder temperatures the carbon dioxide and water molecules slow down and are not moving as quickly as active when they are frozen. This allows the carbon dioxide molecules to be trapped in the water. Until the carbon can get enough energy to break free, the molecules are trapped inside the water. The carbon dioxide will eventually break free and all of it will find its way out of the soda completely. When you shake a can of soda, you help the carbon dioxide break out of the water cages and it will shoot out of the can when you open it.