The ice cools the can and the air around it. As air cools, it condenses, or changes from water vapor into a liquid. This is one step of cloud formation. Dew eventually forms as the water vapor condenses on the side of the can. In the atmosphere, the water vapor condenses onto tiny dust, dirt, pollens and pollutants that we call condensation nuclei. Once this happens, the tiny water droplets collide with each other, eventually becoming big enough for us to see in the form that we know as clouds.
When enough water vapor (moisture) is present on a cool night, some of the water vapor will condense onto grass, cars and other surfaces. The water vapor changes from a gas, to a liquid, called dew droplets.
When salt is added to our experiment, it cools the temperature below freezing. Instead of dew forming on the can, frost forms. On a freezing night when enough water vapor is present, it can change into the solid state and form frost. Frost can cause significant damage to crops.