Anhydrous calcium chloride (CaCl₂) is used in a desiccator because it is an effective drying agent that readily absorbs moisture from the air.
The Power of Anhydrous CaCl₂
Desiccators are sealed containers used to maintain a dry atmosphere for storing moisture-sensitive substances. The drying agent placed inside absorbs water vapor, keeping the internal environment dry. Anhydrous or fused calcium chloride is a common choice for this role due to its specific chemical properties.
Key Properties Explained
The effectiveness of anhydrous CaCl₂ as a drying agent stems from two main properties:
- Highly Hygroscopic: This means it has a strong affinity for water and readily absorbs moisture from its surroundings, even from the air.
- Deliquescent: As it readily absorbs moisture, it continues to do so until it dissolves in the absorbed water, forming a solution. This indicates its capacity to absorb significant amounts of water.
As stated in the reference, "Anhydrous or fused calcium chloride is highly hygroscopic in nature. It readily absorbs moisture and it is deliquescent in nature so it is used as a drying agent in a desiccator."
How it Works in a Desiccator
When anhydrous CaCl₂ is placed in the base of a desiccator, it actively pulls water vapor from the air within the chamber. This process lowers the humidity, creating a dry environment suitable for:
- Storing dry chemicals to prevent them from absorbing moisture (hygroscopic substances).
- Drying solids after filtration or other processes.
- Protecting sensitive equipment or samples from humidity.
The absorbed water becomes chemically bound to the CaCl₂, forming hydrated calcium chloride (e.g., CaCl₂·nH₂O). Because it is deliquescent, it can absorb enough water to turn into a liquid solution over time, which is why it is typically placed in the bottom compartment of a desiccator, separate from the items being dried or stored.
In summary, anhydrous CaCl₂'s ability to absorb moisture due to its hygroscopic and deliquescent properties makes it an excellent and widely used drying agent in desiccators.
