Winter conjures many wonderful things to our imaginations. Snow covered hills, warm jackets and mittens covered in shimmering snow, and icycles dangling down from rooftops creating a magical winter wonderland! Of course, while much of the country is inundated with icy conditions, snow days, and freezing temperatures, those of us who live in dry areas may find ourselves longing for a way to experience some of that icy play for ourselves! With these experiments, you can bring a winter blast of frozen science right into your home, wherever you live, no matter what time of year! All you need is some ice, salt, food coloring, and you’ll be ready to dive into the properties of chemistry and physics with a hefty dose of creativity!
CARVING ICE SCULPTURES WITH ROCK SALT!
Optional: Kosher salt and table salt
Fill your balloon with tap water from the sink. Then, put it in your freezer and leave it to freeze overnight.
The next day, unwrap the balloon to reveal a frozen ball of ice! Set your frozen iceball on to your bowl and prepare your salts and food coloring.
Place some rock salt on top of the ice ball. Observe what happens as the salt makes contact with the ice. Sprinkle a small amount of kosher salt onto a different area of the ice ball. If you have table salt on hand, do the same with that. Do you notice any differences when salt crystals of different sizes interact with the ice ball?
Place a few handfuls of rock salt into the bowl and set the ice ball on top of it. Allow it to rest on top of the salt for about five minutes, then shift the ice ball so a different area can be coated by the salt. Do you notice any changes as the ball of ice is left to sit on the salt?
After about 10 or 15 minutes, you should see some nice canyons, valleys, and carvings begin to form on your ice ball. Carefully examine the surface of the ball, and then drop one drop of food coloring into any feature you see.
Use a variety of colors to bring out the changing surface on your ice ball! You can even create your own splashes of watercolor ice art by mixing colors as they blend into each other through the rivers and valleys of your ice!
Take it Further!
If you have a flat small bowl or petri dish, freeze a small amount of water (enough to cover the bottom of the bowl) to create a flat frozen disc. To loosen the disc from the bowl or petri dish, simply place the bowl in some warm water (do not get the water on the ice!) to loosen it until it comes out. Then, you can place various salt crystals on the surface of your flat disk to create a colorful frozen sun catcher!
After your finished with your creative ice play, it’s time to put your salt to work with some chemistry, physics, and ice cream!
MAKE YOUR OWN ICE CREAM!
1/2 cup half and half or heavy cream
2 tbsp sugar
1/2 tsp vanilla extract
3 cups ice
1/2 cup rock salt
1 gallon sized freezer bag
1 sandwich bag
(Sugar free option: replace sugar and vanilla with sugar free vanilla syrup, or sugar free simple syrup and vanilla extract)
Pour half and half, sugar, and vanilla into your small sandwich bag. Close the bag so that it is airtight and completely sealed.
Place the sandwich bag into the gallon sized freezer bag. Then, add the ice and the salt into the freezer bag. Seal the bag, leaving a small amount of air inside, but make sure it is sealed tightly closed.
Shake the freezer bag for about 7-10 minutes, so that the ice and salt move across the bag with the liquid mixture. Shake it in all kinds of directions, and any way you like, just as long as you keep shaking it constantly until the liquid has reached a preferred ice cream state. You can stop every once in a while to feel the bag of liquid and see if it is to your liking.
Once you’ve reached your preferred ice cream consistency, open the freezer bag and pull out your ice cream bag. Give it a quick rinse with some cold water to remove all of the salt. Open the bag, pour out your ice cream, and enjoy!
Take it Further!
Try adding small pieces of fruit to your ice cream! Add a coule of drops of red food coloring with some small diced strawberries for a delicious fruity treat! You can also try adding cocoa, chocolate chips, coconut, or any other additions to your ice cream.
If you want to make this an experiment, try this with different sized salt crystals. Will this process take longer with kosher salt or table salt? What if you were to skip the salt entirely? Would you still get the same result, a delicious bowl of frozen ice cream?
You may have noticed during your ice cream shake up, that as you were moving the salt and ice around, the ice was melting as your ice cream was freezing up! Or, when you were creating your ice sculptures, that the ice was melting even as it seemed to grow colder to the touch! Next up, we’ll explore why salt melts ice in the first place, as well as why it can feel so much colder in your hands while you’re working with it.
In colder climates, salt is often used on icy roads to melt the ice to make the roads safe for transportation. This works because salt lowers the freezing point of ice, which will turn it into a liquid instead of a solid, even at freezing temperatures! In order to examine how this works, we first need to understand the crazy interplay of atoms, molecules, and heat energy that occurs when ice is formed!
Ice forms as the temperature of liquid water drops to freezing, at 0° Celcius or 32° Farenheit. This slows down the motion of molecules in the water until they lock together in a crystalline structure, the solid form of water known as ice! If an ice cube is left on a counter top, the heat energy of the surrounding environment can break apart the bonds between these molecules, causing them to move faster and melt into liquid water.
There is actually an interesting game of tug of war that occurs here, as the atoms are attracted to other atoms still locked into the ice structure! So, you have some molecules ’’being grabbed’’ by the ice, while others are being broken apart by the heat from the surrounding environment. Whichever force is the strongest, wins! If the temperature is low enough to allow the crystal formation to lock and build, then ice will reform and rebuild a solid shape. If the temperature is too warm, too many molecules get broken apart from that structure, causing the ice to melt.
So what does salt have to do with it? When you add something like salt to ice, it interferes with the melting and refreezing that happens on the molecular level in the ice cube. Suddenly, there’s something in the way of the ice structure, and even though the temperature is cool enough, it can’t lock onto these atoms that are floating around as liquid water. So instead of refreezing, the water melts away! This is why the freezing point of ice gets lowered, water that would otherwise remain frozen at 0° Celsius or 32° Farenheit turns to a liquid because the ice has disrupted the molecules’ ability to latch on to each other and retain that solid form.
Why Does Salt Make Melted Ice Colder?
When a substance changes phases of matter (solid, liquid, gas, etc), energy is used as molecules change shape to make different structures. Believe it or not, as water freezes and molecules slow down and lock into position in a crystal structure, it actually takes quite a bit of energy to keep them locked in place! When ice melts, this energy is released as small amounts of heat energy. When you add salt to ice, it lowers the melting point of the ice. So, the ice, already at 0° Celsius, or 32° Farenheit, gives off some of the heat energy it has retained in it’s ice structure. As this heat is given off, the water drops in temperature, even as the ice is melting. In fact, the water can quickly reach a temperature of -20° celsius or -6° farenheiht by the process of releasing heat as it’s melting!
This is also why you should never experiment with ice and salt on your skin. When ice is pressed against your skin, it holds an uncomfortable, but relatively safe 0 degrees. But if you add a layer of salt on your skin, you can quickly drop that temperature to frostbite range, and give yourself frost burns, or even scars! So when you experiment with ice and salt, take care not to let the ice linger on your skin for longer than a few seconds.