Monday, November 29, 2010

How does salt melt ice?

We had to put salt on the step this morning and we see it is now a puddle of water.

Why is this? How does salt melt the ice?

There we learned that the answer has to do with melting points. Most people know that water freezes at a temperature of OºC. Salt dissolves fairly rapidly in ice, lowering its freezing point in an effect known as freezing point depression, and melting it in the process.

You've also probably noticed the effect of salt water on freezing points if you've tried to make ice cream or if you've wondered why the ocean doesn't freeze at the same time as bodies of fresh water, such as rivers, lakes, and ponds.
On a roadway, this means that if you sprinkle salt on the ice, you can melt it. The salt dissolves into the liquid water in the ice and lowers its freezing point.

If you ever watch salt melting ice, you can see the dissolving process happen -- the ice immediately around the grain of salt melts, and the melting spreads out from that point.

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