Fill a balloon with water and freeze it. Put the resulting blob of ice in a large glass baking dish. Set up a ramekin of salt along with eye droppers and liquid food coloring, and get ready to start experimenting.
This Melting Ice with Salt video shares a simple experiment for kids. It’s demonstrated by The Dad Lab‘s Alex and Max with some help from dad Sergei Urban. The London, England-based team films crafts, activities, and science experiments that are fun and easy to try at home.
The food coloring helps observers see how the ice is melting. The large block deters kids from handling the salt and ice in their hands. Safety note: The layer of salt on ice can cause frostbite with prolonged exposure, dropping the ice’s temperature to -21C (-6F). The science from Britannica.com:
But you may be asking how salt lowers the freezing point of water. This concept is called “freezing point depression.” Essentially, the salt makes it harder for the water molecules to bond together in their rigid structure. In water, salt is a solute, and it will break into its elements. So, if you’re using table salt, also known as sodium chloride (NaCl), to melt ice, the salt will dissolve into separate sodium ions and chloride ions.
Often, however, cities use calcium chloride (CaCl2), another type of salt, on their icy streets. Calcium chloride is more effective at melting ice because it can break down into three ions instead of two: one calcium ion and two chloride ions. More ions mean more ions getting in the way of those rigid ice bonds.
Unfortunately, chloride is superbad for the environment. It can kill aquatic animals, and that can thereby affect other animal populations in their food web. Chloride also dehydrates and kills plants and can alter soil composition, making it harder for vegetation to grow. While some other compounds that can melt ice and snow don’t include chloride, they are much more expensive than sodium chloride or calcium chloride.
Here’s another quick video example from Primrose Preschool:
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