Two weeks ago, we talked about how to determine if it is cold where you live, and we talked about salt. We talked about why the Department of Transportation puts salt all over the roads and why businesses coat their parking lots and sidewalks with it, which causes my awesome Virginia Tech rug to look like this:
If you missed Wintry Science – Part 1, feel free to go check it out. In it, I gave you an assignment to figure out what salt does when it comes into contact with ice. Did you try it?
Well, here’s what happened when we performed the experiment:
We started with three containers and three pieces of ice.
Then Princess poured salt—mostly—into the cups.
Cup #1 – Control – No salt Cup #2 – one teaspoon salt Cup #3 – two teaspoons salt
Then we waited, checking the ice every five minutes.
Want to see something totally amazing?
Take a look at our control cup.
Control at 1 minute At 15 minutes At 30 minutes
Now look at cups two and three, with one and two teaspoons of salt, respectively.
Do you see what a difference there is? In the control cup, the ice barely melted after thirty minutes sitting on my counter. However, in the same amount of time, when we added a little salt to cup #2 the ice was almost gone, and when we added twice as much salt to cup #3 the ice completely melted!
For those of you who tried this at home, you saw similar results.
The real question here is “why did this happen?” Did the salt heat up the ice in some way? If you measured with a thermometer, perhaps you were surprised to see the temperature of the water actually go down in the salt-water mix. Why was that?
Well, you know that water freezes at 32 degrees Fahrenheit, but what you may not know is that this freezing point only applies to pure water, or water that doesn’t have anything added to it. When we added salt to the ice, it lowered the freezing point of the water. This is why we could see the ice melt faster and the water temperature get colder. Because of the addition of the salt, the water could not freeze (or remain frozen) at 32 degrees.
This is because when water is cooled, the water molecules move more slowly. If the water gets cold enough, the molecules will slow down so much that the water actually changes state and becomes ice. If salt is added to this water, the water molecules now have friends—salt molecules—and it will take longer for them to get cold and slow down enough to make ice, so the water will get colder before it freezes. Since the freezing point of salt water is lower than the freezing point of plain water, adding salt to water that is already frozen will cause it to melt faster, or—as in the case of the Department of Transportation—it will prevent melting snow from refreezing as quickly, keeping the roads ice-free longer!
So, here we have a renewable resource that can assist us when we want to go out in winter weather safely. It doesn’t require electricity or any other power source, and is not complicated to use. A big truck can drive down my street spreading salt, and in the morning my husband can get to work without sliding on ice. How cool is it that? God made it so that something as simple as salt would melt ice? He must have planned this way to help keep us safe!
Michelle, a Virginia native, currently lives in Pennsylvania with her husband and three children. Active in Scouts, area homeschool groups, and with her family, she can be found on her blog, “Homeschooler on the Edge,” as well as Facebook, Twitter, and Pinterest.