Why Salt Melts Ice

This is the only experiment where I highly recommend setting up a camera (or your phone) to get a time-lapse.  You can see my time-lapse here! Now that I’m putting all of this together, I realize I should have recorded when I put the salt on the ice so you could see that. OOPS. I put one packet of salt (think about the packets that come in plastic wear) on the ice cube on the right side of this video.

In the winter when the road ices over or snow is falling and creating slick roads, we often say the roads are being “salted” or “treated” to help the ice melt.   Here’s how this works: before snow starts to fall, Plan A is to pre-treat the roads.  Road crews lay down a salt mixture on the road (unless it’s going to rain first, which would wash it all away) to prevent ice from forming.  After the snow has already started to fall and the road is icing, road crews are out again sprinkling more salt mixture on top of the ice.  That mixture isn’t quite the same as the salt you put on your food, but that will work for this experiment.  

What you need: 

Salt

Ice (as much or little as you want – I only did this with one ice cube, you can do it with more)

What you do: 

-Make two piles of ice. Again, I just used one cube on each side, but you can do more! Just make sure your piles are equal. 

-Sprinkle salt on ONE pile of ice.  The pile with no salt is your “control” side, showing what would happen to the ice if you didn’t interfere at all.  Be generous with your salt.  Pretend you are salting the road during a snowstorm – just a little salt won’t help much. 

-Watch what happens.  This is the part where the time-lapse helps because this takes a couple hours to play out even with just one ice cube. 

The salt causes the ice to melt faster because CHEMISTRY. I will not pretend to be a chemistry expert, so here’s the basic version:

• the ice makes contact with the surface of the ice and forms a brine (salty water mix) with the molecules there on the surface.

• that salt brine lowers the freezing point of the ice because it makes it harder for the water molecules to stick together and freeze, so it makes it difficult for more ice to form on top of that and it helps to melt the existing ice. Instead of the ice freezing at 32 degrees, when salt is added, ice won’t freeze until the temperature drops closer to 15 degrees.