Calcium chloride reacts with moisture through a physical process of absorption and dissolution, rather than a chemical reaction. Anhydrous calcium chloride is highly effective at absorbing moisture from its surroundings and subsequently dissolves in the water it has absorbed.
The Nature of the Reaction
Contrary to what might be assumed for an interaction between a chemical compound and water, the process involving calcium chloride and moisture is not a chemical reaction that alters the molecular structure of the calcium chloride. Instead, it is a physical reaction. This means that while calcium chloride changes its state (from solid to liquid solution), its fundamental chemical identity remains calcium chloride.
The core characteristics of this interaction are summarized below:
| Aspect | Description |
|---|---|
| Type of Reaction | Physical (not chemical) |
| Initial State | Anhydrous Calcium Chloride (solid) |
| Interaction | Absorbs moisture from the environment |
| Outcome | Dissolves in the absorbed water, forming a solution |
Key Properties: Hygroscopy and Deliquescence
The interaction of calcium chloride with moisture is governed by two key properties:
- Hygroscopy: Calcium chloride is a hygroscopic substance, meaning it readily attracts and holds water molecules from the surrounding atmosphere. This strong affinity for water makes it an excellent desiccant.
- Deliquescence: Beyond just attracting moisture, anhydrous calcium chloride is also deliquescent. This term describes its ability to absorb enough moisture from the air to dissolve completely in the absorbed water, forming a liquid solution. This process often releases a significant amount of heat, making it an exothermic reaction.
Mechanism of Moisture Absorption
The process unfolds in a straightforward manner:
- Moisture Absorption: When exposed to humid air or direct water, anhydrous calcium chloride (CaClâ‚‚) crystals begin to absorb water molecules from the environment.
- Dissolution: As more water is absorbed, the calcium chloride then dissolves in this absorbed water, creating a calcium chloride solution (brine).
- State Change: The solid calcium chloride transforms into an aqueous solution as it continues to draw in moisture until an equilibrium is reached with the ambient humidity.
Practical Implications and Uses
The strong moisture-absorbing properties of calcium chloride make it incredibly useful in various applications:
- Dehumidification: Calcium chloride is widely used as a desiccant in moisture absorbers for homes, basements, and storage areas. It effectively reduces humidity, preventing mold growth, mildew, and moisture damage.
- Dust Control: On unpaved roads and construction sites, calcium chloride is applied to suppress dust. Its deliquescent nature causes it to absorb atmospheric moisture, creating a damp surface that binds dust particles and prevents them from becoming airborne.
- De-icing and Freeze Prevention: While primarily known for lowering the freezing point of water, calcium chloride's initial interaction involves absorbing ambient moisture or existing ice/snow, forming a brine that then works to melt ice. This property makes it a highly effective de-icer for roads, sidewalks, and driveways.
- Industrial Drying: In industrial settings, it's used to dry gases and liquids due to its efficiency in removing water.
Handling and Storage
Given its strong affinity for moisture, anhydrous calcium chloride must be stored in airtight, moisture-proof containers to maintain its effectiveness. Exposure to open air will quickly cause it to absorb moisture, clump, and eventually dissolve, rendering it less effective for its intended purpose. Proper handling also includes using gloves as the dissolution process is exothermic and can cause skin irritation.
