Calcium chloride (\(\text{CaCl}_2\)) is highly hygroscopic, meaning it readily attracts and retains water molecules from the surrounding air. This common salt is utilized across various settings because of its strong affinity for water. It is a crystalline, white substance often encountered commercially in the form of pellets, flakes, or granular powder, designed to maximize the surface area exposed to humidity.
The Process of Deliquescence
Calcium chloride demonstrates deliquescence, a moisture-absorbing behavior that is a more aggressive form of hygroscopy. Deliquescence occurs when a substance absorbs so much atmospheric moisture that it eventually dissolves itself completely, forming a liquid solution known as a brine. The process starts when the solid \(\text{CaCl}_2\) crystals draw in water vapor.
This powerful attraction is due to the salt’s ionic nature, where calcium and chloride ions strongly bond with polar water molecules. As the salt absorbs moisture, water molecules surround the ions, gradually breaking down the solid crystal structure. Deliquescence continues as long as the vapor pressure of the forming solution is lower than the partial pressure of water vapor in the air.
The compound stops absorbing moisture only when equilibrium is reached between the solution’s vapor pressure and the ambient water vapor pressure. In a humid environment, the solid salt will continue to pull in water until it becomes a puddle of liquid brine. Calcium chloride can absorb a substantial amount of moisture, with some forms taking in up to three times their own weight in water.
Practical Applications of Calcium Chloride
The ability of calcium chloride to aggressively absorb and retain moisture makes it valuable in commercial and industrial applications.
One common consumer use is in dehumidifiers and desiccants for moisture control in enclosed spaces. These products are placed in homes, storage units, or specialized packaging to lower humidity and protect goods like electronics or textiles from damage.
Another widespread use is for dust control on unpaved roads and construction sites. When \(\text{CaCl}_2\) flakes are applied, the resultant brine solution acts as a binder, keeping fine dust particles heavy and preventing them from becoming airborne. The deliquescent nature of the salt ensures the surface remains damp by continuously drawing moisture from the air, maintaining air quality and road stability.
In industrial settings, high-purity anhydrous calcium chloride serves as a drying agent for gases and liquids where trace moisture must be removed. This is important in the petrochemical industry, where moisture can cause undesirable reactions. It is used to dry gases like nitrogen, oxygen, and hydrogen, ensuring the integrity of processes that require extremely low humidity.
Safe Handling and Storage
Calcium chloride requires specific handling and storage procedures to maintain its effectiveness and ensure safety. When the solid compound contacts water, it undergoes an exothermic reaction, releasing heat. If large quantities are mixed, this heat release can be significant and potentially cause thermal burns.
Contact with the skin or eyes should be avoided, as the compound can cause irritation. Appropriate personal protective equipment, such as safety goggles and gloves, is recommended to prevent direct exposure.
To prevent the product from dissolving itself, calcium chloride must be stored in a cool, dry area away from any source of moisture. Containers must be kept tightly sealed and airtight to prevent exposure to atmospheric humidity.