Calcium Chloride vs. Calcium Chloride Dihydrate — What's the Difference?

Calcium Chloride and Calcium Chloride Dihydrate are both chemically classified as salts, but they differ primarily in their water content. Calcium Chloride is anhydrous, meaning it does not contain water molecules bound to its ions. Conversely, Calcium Chloride Dihydrate includes two molecules of water as part of its chemical formula, specifically CaCl2•2H2O. This means that in addition to the calcium and chloride ions, there are water molecules integrated into its crystal structure.

Calcium Chloride, being anhydrous, has a high affinity for water and is, therefore, often used as a desiccant to absorb moisture in various applications. In contrast, Calcium Chloride Dihydrate, with its already present water molecules, has different properties and applications. The presence of water in Calcium Chloride Dihydrate impacts its physical properties, like its melting point, which is lower than that of anhydrous Calcium Chloride.

In terms of application, Calcium Chloride is widely utilized in industries such as food, construction, and road maintenance, where its ability to depress the freezing point of water is beneficial. Calcium Chloride Dihydrate, on the other hand, may be preferred in situations where the presence of water is beneficial or required, such as in certain laboratory applications or in medical uses. Thus, the choice between the two can often depend on specific application needs.

Physically, Calcium Chloride appears as white, hard fragments or flakes, while Calcium Chloride Dihydrate usually presents as a white, crystalline solid. The dihydrate form typically appears more powdery or granulated due to the water content within its crystals. Therefore, physical appearance might often be a visual clue to distinguish between Calcium Chloride and Calcium Chloride Dihydrate.

The difference in water content between Calcium Chloride and Calcium Chloride Dihydrate can significantly impact their respective behaviors, especially in solutions. Calcium Chloride is notably hygroscopic and quickly dissolves in water, releasing a lot of heat in the process. Calcium Chloride Dihydrate, however, due to its existing water molecules, may dissolve differently and exhibit a different heat of solution compared to its anhydrous counterpart.