Calcium Chloride Anhydrous VS Dihydrate! What is The Difference?

Calcium chloride (CaCl₂) is a versatile chemical compound widely used in various industries, including food, pharmaceuticals, construction, and more. It exists in different forms, primarily as anhydrous calcium chloride and calcium chloride dihydrate. Understanding the differences between these two forms is crucial for selecting the appropriate type for specific applications. This article delves into the key distinctions between calcium chloride anhydrous and calcium chloride dihydrate, focusing on their chemical properties, physical characteristics, and common uses.

Anhydrous Calcium Chloride

  • Chemical Formula: CaCl₂
  • Molecular Weight: 110.98 g/mol
  • Structure: Anhydrous calcium chloride is a simple ionic compound consisting of calcium cations (Ca²⁺) and chloride anions (Cl⁻) without any water molecules attached.

Calcium chloride is an inorganic compound containing CaCl2. It is the chloride salt of calcium metal. Furthermore, this compound occurs as a white crystalline solid at room temperature. It is highly water-soluble and it is highly hygroscopic. This makes anhydrous calcium chloride an excellent desiccant. Calcium chloride usually exists in hydrated forms. i.e. CaCl2(H2O)x, where x = 0, 1, 2, 4, and 6.

anhydrous calium chloride
The Calcium Chloride Anhydrous prills

Anhydrous Calcium Chloride has the following uses:

  • De-icing: Widely used as a deicing agent to prevent ice formation on roads, sidewalks, and other surfaces.
  • Food Additive: Employed as a food additive for various purposes, such as a firming agent and to enhance texture.
  • Desiccant and Drying Agent: Its highly hygroscopic nature makes it an effective desiccant and drying agent in applications where moisture control is critical, such as packaging, shipping, and industrial product manufacturing.
  • Concrete Accelerator: Used in concrete mixtures to accelerate the initial setting time, improving construction efficiency.
  • Heat Packs and Self-Heating Cans: Due to its high heat of dissolution, anhydrous calcium chloride is utilized in heat packs and self-heating cans for generating warmth.

However, it is important to note that anhydrous calcium chloride is an irritant and can cause skin irritation. Additionally, excessive consumption can lead to hypercalcemia, a condition characterized by elevated calcium levels in the blood.

Regarding its production, anhydrous calcium chloride can be obtained as a byproduct of the Solvay process, which primarily uses limestone as a raw material.

Dihydrate Calcium Chloride

  • Chemical Formula: CaCl₂·2H₂O
  • Molecular Weight: 147.01 g/mol

Calcium chloride dihydrate is an inorganic hydrated compound, that contains about 20% chemically combined water, known as water of crystallization. When considering the structure of this compound, it has one calcium chloride molecule in association with two water molecules. This dihydrate form naturally occurs as the rare evaporate “sinjarite”.

dihydrate calcium chloride
The Calcium Chloride Dihydrate Flakes

Dihydrate calcium chloride is used in applications that require a controlled moisture level, such as in concrete acceleration, brine for refrigeration, and as an additive in food preservation. Its lower hygroscopicity makes it easier to handle in certain environments.

Calcium Chloride Anhydrous VS Dihydrate

Differences and Comparisons

Calcium chloride (CaCl₂) is an inorganic compound, whereas calcium chloride dihydrate is its hydrated form with the chemical formula CaCl₂·2H₂O. The primary difference between the two is that calcium chloride is anhydrous, meaning it contains no water molecules, while calcium chloride dihydrate includes two water molecules. Consequently, the molecular weight of the dihydrate form is 36 g/mol greater than that of the anhydrous form due to the additional water molecules.

Both also contain trace amounts of Bromide and both contain small amounts of Potasium Chloride (2 to 3%) and Sodium Chloride (1 to 2%). 

Anhydrous calcium chloride appears as a white crystalline solid, often in granular or powder form, and is highly hygroscopic, meaning it readily absorbs moisture from the air. It has a melting point of 772°C, a boiling point of 1935°C, and a density of 2.15 g/cm³. In contrast, calcium chloride dihydrate appears as a white or off-white crystalline solid, typically in flake form, and is also hygroscopic but less so than the anhydrous form. It has a melting point of 175°C (decomposing upon further heating) and a density of 1.85 g/cm³.

The primary differences between anhydrous calcium chloride and dihydrate calcium chloride lie in their water content and hygroscopic properties:

  1. Hygroscopicity: Anhydrous calcium chloride is more hygroscopic, absorbing more moisture from the air compared to dihydrate calcium chloride.
  2. Applications: Anhydrous calcium chloride is ideal for moisture-sensitive environments and rapid drying, whereas dihydrate calcium chloride is better suited for applications requiring moderate moisture absorption and easier handling.
  3. Heat of Dissolution: Anhydrous calcium chloride releases more heat upon dissolving in water, making it suitable for exothermic reactions in heating applications.

Different Application Areas

  • Moisture Control: For packaging, shipping, and industrial drying, anhydrous calcium chloride is preferred due to its superior moisture absorption capacity.
  • Concrete Acceleration: Dihydrate calcium chloride is often used in concrete acceleration to ensure a controlled setting process without excessive moisture uptake.
  • Refrigeration Brine: Dihydrate calcium chloride is used in refrigeration systems where a stable brine solution is needed.
  • Food Preservation: In food preservation, dihydrate calcium chloride is favored for its controlled moisture absorption, ensuring product integrity.

When selecting anhydrous and dihydrate calcium chloride, users should consider the specific needs of their process and product. Pay attention to factors such as moisture sensitivity, handling requirements, and desired heat of solution to make your selection.


By gaining a deeper understanding of the characteristics, uses and differences of the two calcium chlorides, readers can better decide to choose the right product in different situations, thereby improving production efficiency and product quality.

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