How Does Salt Work?

Salt lowers the freezing point of water; this causes ice to melt even if the temperature is below its normal freezing temperature. 

The freezing point of water is 0^oC. Therefore, when it reaches below that point, the bonds between the water molecules grows stronger and the molecules arrange themselves in a crystalline structure thereby creating ice. When it reaches above 0^oC the opposite happens and the bonds become weaker, and the structure returns to fluid. 

When rock salt is applied to ice, it dissolves into sodium and chloride ion which loosen the bonds between the ice’s hydrogen ion thereby turning the ice back into water. 

However, once the pavement temperature reaches below -12^oC, regular salt (NaCl) becomes much less effective.