How to Make a Soda Slushy
Super Cooled: An aqueous solution is super cooled when it is liquid at a below the freezing point of water (32oF (0 oC).
Crystal: Solid, 3-D matter made up of atoms, molecules, or ions in a regularly ordered pattern.
Crystallization: The process of matter changing into a solid crystal state;
Pressure: A measure of the force being exerted over an specific area of matter; The pressure of gases inside a sealed soda bottle, is the force of the gases on the surface area of the liquid soda. The more gas inside the sealed bottle, the greater is the gas pressure on the liquid.
Shaking a sealed soda bottle increases the gas pressure inside the bottle. This is because carbonated sodas, such *Coke, have a high concentration of carbon dioxide gas dissolved in the liquid. When carbon dioxide gas dissolves in the liquid soda, it is said to be a carbonated soda.
An increase in pressure on a liquid causes the liquid to have a lower freezing point. At normal atmospheric (air) pressure at sea level, the freezing point of pure water is(32oF (0 oC). Soda is a solution made of water with dissolved carbon dioxide and flavoring. The dissolved materials in the water makes the soda solution have a lower freezing point. This means that the freezing point of the soda is lower than the freezing point of pure water.
Shaking the soda releases some of the dissolved carbon dioxide gas molecules, thus the freezing point of the new solution goes up a little. But, the released carbon dioxide gas increases the gas pressure within the sealed body and lowers the freezing point of the liquid soda solution. There more stuff going on, but the bottom line is that the increase in pressure has more effect than the amount of gas dissolved. Thus the freezing point of the liquid soda solution is very low. This is referred to as being super cooled.
A super cooled solution is very unstable. This means that the dissolved materials easily “falls out of solution.” This means that the dissolved materials, such as gases, leave the liquid solution and mix with the gases outside the solution. The dissolved solid and liquid molecules will leave the liquid solution and form solid crystals.
If a sealed bottle of super cooled soda is shaken, it forms what looks like a slushy, which are flavored icy crystals mixed with gas molecules.
If you carefully open a super cooled bottle of soda and pour it into a chilled container, there will be some slushy formed, but you must add energy by stirring for the entire super cooled soda to crystallize into a slushy. A bowl at room temperature provides the energy required for the soda to crystallize forming a slushy.