Have you ever wondered why putting chemicals like salt on a road makes the ice melt?
To see how NaCl (table salt) melts ice by lowers the melting temperature of water, you’ll need an ice cube, a glass of water, and a piece of kitchen twine or string about 6 inches long and salt.
What to do:
Drop an ice cube in a glass of ice water. Try to pick the ice cube up without your fingers by simply placing the string on it and pulling up. Impossible, right?
Now, dip the string in water, lay it across the ice cube and sprinkle a generous amount of salt over the string/ice cube. Wait about a minute and try again to lift the cube using only the string. What happens?
It may seem like magic, but it’s only science. Watch me demonstrate the experiment by clicking here.
Salt lowers the temperature at which ice can melt and water can freeze. Usually, ice melts and water freezes at 32 degrees Farenheit, but if you add salt to it, ice will melt at a lower (colder) temperature.
The salt helps the ice surrounding the string start to melt, and it takes heat from the surrounding water, which then re-freezes around the string.
Different chemicals change the freezing point of water differently. Salt can thaw ice at 15 degrees F, but at 0 degrees F, it won’t do anything. Other de-icing chemicals they add to roads can work at much colder temperatures (down to 20 degrees below zero.) If it’s cold enough, even chemicals won’t melt the ice.
Pressure can also make ice melt at colder temperatures. This is why ice skates glide on rinks. The pressure is constantly melting the ice a where the blade presses down on it so the blade glides on a thin layer of water!
Grab your coat and head outside to try this fun winter science project!
A large plastic zipper bag
Cotton kitchen twine
a toothpick or wooden skewer
a spray bottle
a squeeze bottle or syringe (optional, but helpful)
a very cold day (below 10 degrees F works best, but you can try it on any day when it’s below freezing)
Note: This experiment takes lots of playing around and results will vary depending on how cold it is outside. Remind your kids (and yourself) to be patient and try it on a colder day if it doesn’t work the first time around! If the bag leaks too quickly, try making one with smaller holes around the string.
What to do:
- Use a toothpick or skewer to poke 3 small holes in the bottom of a zipper plastic bag. Make one in the middle and one on each end.
- Cut three long (3 feet or so) pieces of kitchen twine and knot them at one end.
- Carefully thread the twine through the holes in the bag so that the knots are inside the bag to keep the strings from falling through. Try to keep the holes from getting too big, since the bag will be filled with water and you’ll want it to drip out very slowly around the string.
4. Attach two more pieces of twine to each top corner of the bag (above the zipper) to use for hanging the bag
5. Go outside and hang the bag from a low tree branch or railing.
6. Tie each of the three strings to something on the ground, like a rock, piece of wood, or the handle of an empty milk carton filled with water to weight it down. Arrange the objects so that the strings loosely radiate out at around a 45 degree angle. (See photo)
7. Add food coloring to some ice-cold water in a pitcher.
8. Fill the spray bottle with ice-cold water.
9. Add the cold colorful water to the zipper bag hanging outside. Zip the top of the back to slow the rate of leaking.
10. Immediately spray the strings with water to guide the leaking water down the strings.
10. Wait for the water on the strings to freeze. Use your syringe to add a little bit more water to the strings (same color) and wait for them to freeze again. Repeat until you have a nice layer of ice/icicles.
11. Refill the bag, using a different color of ice-cold water. Spray the strings lightly again. Repeat step 11.
12. Add layers of color to the icicles until you’re happy with the way they look!
The science behind the fun:
Icicles form when dripping water starts to freeze. Scientists have discovered that the tips of icicles are the coldest part, so that water moving down icicles freezes onto the ends, forming the long spikes you’ve seen if you live in a cold climate. When you add different colors of water to icicles in sequence, the color you add last will freeze onto the tip of the ice.
You’ll find more fun ice science experiments in my book “Outdoor Science Lab for Kids” and in my upcoming books “STEAM Lab for Kids” (Quarry Books April 2018) and “Star Wars Maker Lab” (DK- July 2018)
Remember this homemade snow candy from Laura Ingalls Wilder’s classic “Little House in the Big Woods?” You can make the same amazing maple treats using heat evaporation and quick cooling in the snow, or on crushed ice cubes.
Here’s how to make the candy, along with some candy-making science, straight from the pages of my new book, “Outdoor Science Lab for Kids,” which you can order from your favorite book retailer by clicking here.
-1 cup pure maple syrup
-fresh, clean snow
Safety Tips and Hints:
-Hot sugar syrup can cause burns. This experiment must be done with adult supervision.
-Allow candy to cool completely before tasting.
-Only use pure maple syrup for the best results.
Step 1: Go outside and scout out a spot with some clean snow several inches deep for making your candy. Alternately, collect and pack down a few inches of fresh snow in a large, flat container, like a casserole dish. (You can use crushed ice cubes if you don’t have snow.)
Step 2. Boil the maple syrup in saucepan, stirring constantly until it reaches around 235-240 degrees F (soft ball stage.)
Step 3. Remove the maple syrup from the heat and carefully pour it into a heat-resistant container with a spout, like a Pyrex measuring cup.
Step 4. Pour wiggly candy lines into the snow to freeze them into shape.
Step 5. When you’re done, remove the candy from the snow with a fork.
Step 6. Eat your candy right away, or let it warm up and wind it around sticks or skewers to make maple lollipops. Enjoy!
The Science Behind the Fun:
Maple syrup is made from watery tree sap boiled to evaporate most of the moisture it contains when it’s first tapped from a tree. Following evaporation, the syrup that remains is mostly made up of a sugar called sucrose, but it also contains smaller amounts of glucose and fructose.
Naturally, other organic compounds are also present in tree sap, giving syrup from different areas unique flavors. Syrup collected earlier in spring when it is cold tend to be light in color and have a mild flavor. As the days get warmer, microbes ferment some of the sugar in the syrup, making it darker and giving it a more robust taste.
In this experiment, you heat maple syrup, evaporating even more water. A super saturated solution forms, which holds more sugar molecules in the liquid than would be possible if you evaporated the water at room temperature.
When you pour the supersaturated sugar into the snow, it cools quickly, forming some sugar crystals to give the maple candy a soft, semi-solid consistency. Heating the syrup to a higher temperature will evaporate more water, resulting in even more crystal formation in the cooled syrup, making it harder to bite. If you carefully evaporate all of the water from maple syrup, you’ll be left with pure maple sugar crystals.
-Try collecting some syrup from your pan at several different temperatures and compare the resulting snow candy for texture, color and consistency.
-Can you do the same experiment with other sugar syrups, like molasses or corn syrup?
-Try to make maple sugar.
It’s been cold in Minnesota. The governor closed all the schools today in anticipation of a high temperature of around 15 below, and a low of close to 30 below in the Twin Cities. And it gets colder as you go North. This morning on Kare 11 Sunrise, we threw boiling water in the air, froze foaming soap, blew ice bubbles and experimented with bologna at 20 below to see why tongues stick to cold metal.
We did the boiling water experiment at the cabin a few weeks ago when it was a balmy 18 below. As you can see, the low viscosity of the water, and the fact that it’s about to evaporates causes most of it to instantly freeze into a snowy fog and a shower of tiny ice crystals.