Definition of Deliquescence
Deliquescence is a phenomenon where a solid substance absorbs moisture from the atmosphere until it dissolves completely in the absorbed water, forming an aqueous solution. This process occurs when the vapor pressure of the saturated solution formed by the substance is less than the partial pressure of water vapor in the surrounding air. Essentially, the substance 'melts' due to atmospheric humidity.
Key Principles and Conditions
For deliquescence to occur, two primary conditions must be met: the substance must be highly soluble in water, and the relative humidity of the environment must be sufficiently high. The critical relative humidity (CRH) is the specific humidity level above which a substance will deliquesce. If the ambient air's humidity exceeds the CRH, the substance will continue to draw in moisture, facilitating its dissolution.
Practical Examples of Deliquescence
Common examples of deliquescent substances include calcium chloride (CaCl₂), sodium hydroxide (NaOH), and potassium hydroxide (KOH). If left exposed to humid air, these compounds will visibly start to absorb water, first appearing damp, then forming a concentrated solution. For instance, calcium chloride is often used as a desiccant (drying agent) because of its strong deliquescent properties, effectively removing moisture from enclosed spaces.
Importance and Applications
Understanding deliquescence is crucial in various fields. In chemistry, it's vital for proper storage and handling of sensitive chemicals to prevent spoilage or changes in concentration. In civil engineering, deliquescent salts like calcium chloride are used as dust suppressants on unpaved roads and as de-icing agents, as their ability to absorb water and lower the freezing point of water is exploited. Conversely, it can be a problem in manufacturing, causing corrosion or affecting product stability.