WHY USE SALT TO MELT ICE ON THE ROADS?

Salt lowers the freezing and melting point of water and ice. The melting point of ice under normal conditions is zero degrees Celsius. Seawater, however, freezes or melts at -2.2 degrees Celsius due to its high salinity.

As to why salt lowers the melting and freezing point of water, this is a bit more difficult to explain without going into some complex chemistry.

Water is made from H2O, and anything else which gets in there, such as sodium in the case of salt, gets in the way and makes it harder for the H O to bond as ice. 2Upon sprinkling salt onto ice, the salt first dissolves into the liquid water surrounding the ice, causing the ice to melt. The salt can only lower the melting and freezing point of water up to around -16 degrees Celsius. If the temperature is below this point then salt is rendered ineffective, and it would be better to pour sand over the ice to help increase traction.