Have you ever wondered how salt actually contributes to ice or snow melting? If you live in a really cold area where the roads, sidewalks and driveways are frequently icy during winter, you have probably used salt to melt the ice and snow on more than one occasion because you KNOW this method works. But, why does it work exactly? Maybe this knowledge was probably passed on from generation to generation or learned from other people around you. It is likely that many people do not actually understand the science of the process, not because they are unable to, but maybe it is just something that they have not really taken the time to think about. This article discusses in detail how salt causes ice and snow to melt, so the next time a curious kid asks you why you are adding salt to the snow on the sidewalk, you will be able to give them an immediate and accurate answer!
Salt, scientifically known as sodium chloride, is soluble in water. This means that when salt is added to water, it dissolves in the water, adding foreign particles to the liquid water. This addition of foreign particles decreases the freezing point of water, i.e. will result in water freezing at a lower temperature than it usually does, below 32°F or 0°C. This effect is known as freezing point depression. If water is able to freeze at a lower point than it normally does, then this results in the ice or snow melting. To understand this further, it is helpful to note that when ice and water interact, there is a rate of melting and a rate of freezing. If the rate of melting exceeds the rate of freezing, then the ice will noticeably melt, whereas the opposite holds true – if the rate of freezing exceeds the rate of melting, then the water will freeze. The addition of salt disrupts the melting/freezing equilibrium of the system. Salt dissolves into the liquid water, preventing these liquid molecules from turning into ice. This decreases the rate of freezing of the system, making the rate of melting greater than the rate of freezing resulting in visible melting of the ice or snow.
Salt is not the only substance that causes ice or snow to melt. Other foreign substances dissolved into water will result in the same melting process occurring. These substances include alcohol, sugar and other salts such as calcium chloride, magnesium chloride and potassium chloride among many others. Salt is probably most used due to it being cheap, easily accessible, and less damaging to the environment than other chemical substances.