Ice cream is delicious, but it is also a really cool example of phase change. Technically, the temperature that the salt lowers is called the freezing point.When a freezing point is lowered, such as by adding salt to water, the process is called freezing-point depression. When the cream changes phases it will change form a liquid to a solid. However, because we will use salt to make this more difficult, the ice cream will stop before it freezes into a solid. As we’ll see in this activity, freezing-point depression is not unique to solutions made of water and salt; it also happens with other solutions. (A solution is made when a substance, such as salt, is dissolved and becomes a solute. The medium into which it is dissolved is a solvent—typically a liquid, like water.) . The secret to making ice cream is to lower the freezing point of ice so it can freeze the cream. How? The scientific secret is plain old salt! Here’s a simple recipe you can follow right at home to make your own ice cream. Try this one with your class.
