How Much of an Effect Does Salt Have on Ice?

Ice and Solutions

• Ice is formed when liquid reaches its freezing point. In fresh water, this temperature is 32 degrees Fahrenheit. There are many factors that can affect this freezing point, however, including the presence of dissolved particles in that water. Anything with a lower freezing point than water that is dissolved into a solution will lower the freezing point of the solution as a whole. For example, sugar dissolved in water will also lower the freezing point, but salt is more widely used because it has a lower cost.

Ice and Concentration

• The freezing point of a solution will change depending on the concentration of salt in the water. A glass of water with a small amount of salt dissolved in it will have a slightly lower freezing point than a glass of fresh water, while the ocean, with a much higher concentration of salt, has a significantly lower freezing point (about 28 degrees Fahrenheit). When ice is spread on surfaces covered in ice, it melts the ice rapidly because it is so highly concentrated.

Sea Ice Formation

• In the ocean, the lower freezing point of salt water and the higher density of salt water have a major effect on the way sea ice is formed. When ice crystals form in the colder water on the surface of the ocean, the crystals push out the salt, raising the concentration of salt in the water beneath the ice. This concentration of dense water beneath the ice allows the ice to float and form sheets of ice that build up over the course of several years.

Practical Applications

• Salt and ice water also have several uses in the home, including making ice cream and rapidly cooling beverages. Because ice water with a high salt concentration has a lower freezing point, it can get cold enough to freeze an ice cream mix (which has a low freezing point because of its sugar content). It can also rapidly cool beverages submerged in it, since the solution can get well below the normal freezing point of water and draw heat from the beverages.