why does salt melt ice

Why Does Salt Melt Ice?

Salt is the primary component in most of today’s ice melter products. Rock Salt, Calcium Chloride, Magnesium Chloride, and Potassium Chloride all contain a considerable amount of salt in them.

If you live in a cold climate  with frequent snowfalls, then you have probably seen people spreading pure salt on sidewalks to melt the snow. This practice has become quite common and you might wonder how the salt is able to melt ice and snow.

Salt Lowers the Freezing Point

Why does salt melt ice?
In a nutshell, salt is a great ice melter because it causes “freezing point depression.” This means that salt helps in lowering the freezing point and, consequently, the melting point of water (the main component of snow and ice). In its pure state, water freezes at 0°C or 32°F. By using salt, that freezing point can be lowered which forces the ice to melt and prevents the water from freezing or re-freezing.

It must be noted, however, that salt alone can’t melt ice. It must first be combined with water to start the melting process. Fortunately, ice and snow are generally covered with a thin film of water. As salt touches this water, it starts to dissolve – subsequently lowering the freezing point and melting the ice surrounding it.  It is because of this process  that most, if not all, ice melters today are made with some quantity of salt.

Perhaps you are also curious why ice melters also make use of different substances like calcium, potassium, and magnesium. These ingredients help in further decreasing freezing points. They also help in reducing tracking and the corrosive characteristics that salt naturally possesses. To give you an idea of how salt solutions work, here is a very short list:

  • With 10% salt solution, water freezes at 20°F (-6°C)
  • With 20% salt solution, water freezes at 2°F (-16°C)

The reason why salt melts ice is quite simple. This melting power is the main reason salt will continue to be used for producing the majority of ice melters on the market today.