The answer to whether salt evaporates with water is no. Evaporation is a natural process where a liquid changes phase to become a gas or vapor. When salt is dissolved in water, the two substances have fundamentally different chemical properties. Only the water will transition into the gaseous state when heated or exposed to air, a separation utilized in several natural and industrial processes.
The Science of Separation
The separation occurs because the forces holding water molecules together are vastly weaker than the forces holding salt together. Water molecules (H2O) are connected by relatively weak intermolecular forces called hydrogen bonds. These bonds require only a small input of energy, such as heat, to break, allowing water molecules to escape the liquid surface and become vapor.
Sodium chloride (NaCl), or common table salt, is an ionic compound held together by a strong electrostatic attraction between positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-). This ionic bond is significantly stronger than the hydrogen bonds in water, requiring far more energy to break. Water boils and vaporizes at \(100^\circ\text{C}\) at standard atmospheric pressure.
In contrast, the temperature needed to turn salt into a gas is extremely high, with a boiling point around \(1,413^\circ\text{C}\). Since water evaporates at a temperature over ten times lower than the salt’s boiling point, the salt ions do not gain enough energy to enter the gas phase. The salt remains as a non-volatile solute, meaning it cannot easily vaporize, and is left behind as the water molecules depart.
The Process of Crystallization
As water evaporates from a salt solution, the concentration of dissolved sodium and chloride ions steadily increases. This eventually leads to the point where the solution becomes supersaturated, holding more dissolved salt than it can normally contain. With the solvent gone, the ions are no longer separated by water molecules.
The sodium and chloride ions are then free to re-establish their powerful electrostatic connection. They fall out of the solution and spontaneously arrange themselves into a stable, ordered three-dimensional structure called a crystal lattice. This process is known as crystallization, and the resulting solid is the pure, dry salt residue.
Practical Uses of Salt Separation
The principle that salt does not evaporate with water is utilized in large-scale industrial water purification, known as distillation or thermal desalination. In these facilities, saltwater is heated to create steam, which is pure water vapor, leaving concentrated brine and salt minerals behind. The collected steam is then cooled, condensing back into liquid form to produce fresh, potable water free of dissolved solids.
This principle is also the foundation of traditional salt harvesting methods used for millennia. Salt marsh farmers divert seawater into shallow, open-air evaporation ponds. The sun drives the water’s evaporation over days or weeks, mimicking the heating process on a massive scale. As the water is removed, the salt concentration rises until the ions crystallize, forming beds of solid, harvestable salt.