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This is a fun, non-toxic project for kids of all ages. All you need is ice, salt, and food coloring.
You can use any type of salt for this project. Coarse salt, such as rock salt or sea salt, works great. Table salt is fine. Also, you could use other types of salt besides sodium chloride (NaCl). For example, Epsom salts are a good choice.
You don't have to color the project, but it's a lot of fun to use food coloring, water colors, or any water-based paint. You can use liquids or powders, whichever you have handy.
- food coloring (or watercolors or tempera paints)
What To Do
- Make ice. You can use ice cubes for this project, but it's nice to have larger pieces of ice for your experiment. Freeze water in shallow plastic containers such as disposable storage containers for sandwiches or leftovers. Only fill the containers part way to make relatively thin pieces of ice. The salt can melt holes all the way through thin pieces, making interesting ice tunnels.
- Keep the ice in the freezer until you are ready to experiment, then remove the blocks of ice and place them on a cookie sheet or in a shallow pan. If the ice doesn't want to come out, t's easy to remove ice from containers by running warm water around the bottom of the dish. Place the pieces of ice in a large pan or a cookie sheet. The ice will melt, so this keeps the project contained.
- Sprinkle salt onto the ice or make little salt piles on top of the pieces. Experiment!
- Dot the surface with coloring. The coloring doesn't color the frozen ice, but it follows the melting pattern. You'll be able to see channels, holes, and tunnels in the ice, plus it looks pretty.
- You can add more salt and coloring, or not. Explore however you like.
This is a messy project. You can perform it outdoors or in a kitchen or bathroom. The coloring will stain hands, clothes, and surfaces. You can remove coloring from counters using a cleaner with bleach.
How It Works
Very young kids will like to explore and may not care too much about the science, but you can discuss erosion and the shapes formed by running water. The salt lowers the freezing point of water through a process called freezing point depression. The ice starts to melt, making liquid water. Salt dissolves in the water, adding ions that increase the temperature at which the water could re-freeze. As the ice melts, energy is drawn from the water, making it colder. Salt is used in ice cream makers for this reason. It makes the ice cream cold enough to freeze. Did you notice how the water feels colder than the ice cube? The ice exposed to the salty water melts faster than other ice, so holes and channels form.