Freezes salt water

Ions of the salt are now released from the crystal lattice. The freely moving water molecules from the liquid film, in turn, are deposited around the salt ions due to their dipole properties and are thereby bound. The liquid surface film is withdrawn from the surface of the ice.

Na + ion with water molecules (sculpt simulation) Start animation

The ice is in dynamic equilibrium with the liquid film on the surface. This liquid film is always reproduced.

Despite the cooling of the salt-water mixture wetting the ice, there is still enough energy available for new water molecules to be released from the crystal lattice of the ice. The water from the liquid film is "consumed" to dissolve the salt, but is therefore constantly replicated. The new, released water molecules release further ions from the salt. These in turn bind the water molecules. In order to maintain the equilibrium on the ice surface, a new film of liquid is created. The result: the ice slowly disappears.

In addition to the process of dissolving the salt, there is also the melting of the ice. Energy is required to dissolve the salt grid and to melt the ice. This is withdrawn from the environment in the form of heat. This lowers the temperature and the salt-water mixture cools down. Temperatures below 0 ° C are reached. During the dissolving process, salt cools the liquid or the ice-water-salt mixture.

The fact that the ice dissolves when salt is added is used for winter road clearance. By spreading salt, snow and ice-smooth roads can be made free of ice again.

Freezing point depression

The addition of salt to water has another consequence: the water molecules are prevented from building up an ice crystal at temperatures below 0 ° C. The salt solution only freezes at much lower temperatures, the freezing point of the water drops. Because the freezing point of a saline solution is -21.3 ° C, no more salt is scattered at lower temperatures - it would be ineffective.