deliquescent

Deliquescent is a term used in chemistry to describe a substance that, when exposed to air, absorbs moisture from the atmosphere and dissolves in the absorbed water to form a liquid solution. The word derives from Latin deliquescere, meaning to melt away or become liquid.

Deliquescence is a specific form of hygroscopic behavior. Hygroscopic materials absorb moisture, but not all of them dissolve in it; deliquescent substances continue to absorb until they dissolve, creating an aqueous phase at the surface or within a thin film.

Common deliquescent substances include calcium chloride and ferric chloride, as well as other highly hygroscopic salts such as magnesium chloride, sodium hydroxide, and potassium hydroxide. The tendency to deliquesce depends on the ambient relative humidity and temperature; many deliquescent salts require only moderately high humidity to begin dissolving.

Applications and hazards: Deliquescent salts are widely used as desiccants and moisture-control agents in packaging, air conditioning, and de-icing applications. Because several of these substances are strongly caustic and can dissolve with release of heat, handling them safely requires appropriate protective equipment and ventilation. The liquid formed can be highly reactive or corrosive, so care is needed in storage and use.

In practice, deliquescence is exploited to remove moisture from environments or to create aqueous reactions directly from solid reagents. In nature, deliquescent materials can form liquid films on salt deposits in sufficiently humid conditions.