Mm, salty

It's that wonderful time of year. You know, the snowy time of year! Of course, the snow isn't all grand - oftentimes, the snow and ice can cause dangerous situations on roads, walkways, and stairs. I'm sure at this time of year, we've all seen salt on one of these surfaces at some time or another. Most of us know that this is to melt the snow and keep ice from forming, but most of us do not know the reasoning behind it.

In the synthesis of chemicals (particularly in undergraduate lab courses), a melting point of the product will often be obtained to test the purity of it. This can be done because chemists are aware of the fact that impurities in any material will lower its melting point from that of the pure material. This melting point depression does not rely on what impurities are present in the material, but rather how much of the impurities is present.

From this, we understand why every winter thousands of surfaces are coated in salt - it lowers the point at which water will freeze, and is effective so long as enough salt is present to drive down the freezing temperature below the temperature of the air and the ground. This same method of lowering a freezing point is how we preserve our cars' engines in the cold weather. Anti-freeze chemicals are added to the water in internal combustion engines, which lower the temperature at which the water would freeze.