Calcium Chloride Dihydrate: FAQs for Lab Use

Calcium chloride dihydrate is a widely used inorganic salt reagent with the formula CaCl₂·2H₂O, valued in research laboratories for its high water solubility, roles as a calcium ion source, and applications ranging from competent cell preparation to cryoprotection and buffer formulation.

Chemical Formula

CaCl₂·2H₂O

Molecular Weight

147.01 g/mol

Appearance

White crystalline solid (hygroscopic)

Solubility in Water

Highly soluble; approximately 745 g/L at 20 °C (anhydrous basis)

CAS Number

10035-04-8

Aladdin SKU

C431167

Sigma Reference

C5080

What Is Calcium Chloride Dihydrate and What Are Its Key Properties?

Calcium chloride dihydrate (CaCl₂·2H₂O, CAS 10035-04-8, MW 147.01 g/mol) is a white, crystalline, highly hygroscopic inorganic salt. It dissociates readily in aqueous solution to provide Ca²⁺ and Cl⁻ ions. The dihydrate form is the most commonly handled hydrate in the laboratory because it is easier to weigh accurately than the anhydrous form, which aggressively absorbs atmospheric moisture.

Key physicochemical properties include high aqueous solubility, exothermic dissolution, and a relatively low melting point for the dihydrate crystal (~29 °C). Its ionic nature makes it compatible with most standard laboratory buffers and biological media when used at appropriate concentrations.

How Do I Prepare Calcium Chloride Solutions for Common Lab Applications?

To prepare a 1 M stock solution, dissolve 147.01 g of calcium chloride dihydrate in approximately 800 mL of ultrapure water, mix until fully dissolved (dissolution is exothermic — allow to cool), then adjust the final volume to 1 L. Filter-sterilise through a 0.22 µm membrane if the solution is intended for cell culture or microbiology work.

For competent bacterial cell preparation, a common protocol uses 60–100 mM CaCl₂ in cold Tris-HCl or HEPES buffer. Always use freshly prepared or verified stock solutions, as calcium ions can precipitate with phosphate-containing media — avoid mixing CaCl₂ directly with phosphate buffers unless specifically required by the protocol.

Molar mass note: Because you are using the dihydrate (MW 147.01 g/mol) rather than the anhydrous salt (MW 110.98 g/mol), always confirm which form is called for in your protocol before weighing.

What Are the Primary Research Applications of Calcium Chloride Dihydrate?

Molecular biology: CaCl₂ is a cornerstone reagent for producing chemically competent E. coli cells. Calcium ions permeabilise the bacterial outer membrane, allowing plasmid DNA uptake during heat-shock transformation.

Cell biology and signalling: Calcium ions are critical second messengers. Researchers use defined CaCl₂ concentrations in imaging buffers and perfusion solutions to study intracellular calcium dynamics, exocytosis, and calcium-dependent enzyme activity.

Biochemistry: Many enzymes (proteases, kinases, phospholipases) require Ca²⁺ as a cofactor. CaCl₂ is added to assay buffers at µM–mM concentrations to support enzyme activity or structural integrity of calcium-binding proteins.

Media and buffer preparation: CaCl₂ is a standard component of physiological saline solutions (e.g., Hanks' Balanced Salt Solution, Tyrode's solution) and is included in many stem cell and primary cell culture formulations.

Cryopreservation and gel formation: Calcium ions cross-link alginate polymers to form hydrogels used in cell encapsulation; CaCl₂ is also used in cryoprotectant cocktails for some cell types.

How Should Calcium Chloride Dihydrate Be Stored and Handled Safely?

Storage: Store calcium chloride dihydrate in a tightly sealed container in a cool, dry place, away from moisture. Because the compound is strongly hygroscopic, exposure to humid air causes caking and weight gain, which will introduce errors in concentration calculations. Desiccants or sealed storage bags are recommended once the original container has been opened. Recommended storage temperature is 2–25 °C; avoid refrigerators without moisture control.

Safety: Calcium chloride dihydrate is considered low acute toxicity for laboratory use. It is a mild irritant to skin, eyes, and mucous membranes. Standard PPE — laboratory coat, nitrile gloves, and safety glasses — is adequate for routine handling. Inhalation of dust should be avoided; work in a well-ventilated area or use a dust mask when handling large quantities. Dissolution generates heat; add solid to water slowly, never water to a large mass of solid in a closed container.

Disposal: Dilute aqueous solutions can generally be disposed of down the drain in accordance with local regulations, as calcium and chloride ions are present in natural water systems. Verify disposal requirements with your institutional EHS office.

Quality, Purity Grades, and Selecting the Right Product

Calcium chloride dihydrate is available in several purity grades. The appropriate grade depends on the application:

• ACS/Reagent grade (≥99%): Suitable for most general laboratory applications, buffer preparation, and non-GMP research.
• Cell culture grade: Tested for endotoxin, heavy metals, and biological performance; recommended for mammalian cell culture, media preparation, and cGMP-adjacent work.
• Molecular biology grade: Low DNase/RNase contamination; suitable for nucleic acid work and transformation protocols.

Aladdin Scientific offers calcium chloride dihydrate under SKU C431167, corresponding to the reference standard C5080. Always review the Certificate of Analysis (CoA) for the specific lot before use to confirm purity, heavy metal limits, and any functional testing results. When in doubt about grade suitability, contact Aladdin Scientific technical support.

Frequently asked questions

What is the difference between anhydrous calcium chloride and calcium chloride dihydrate?

Anhydrous calcium chloride (CaCl₂, MW 110.98 g/mol) contains no water of crystallisation and is more aggressively hygroscopic, making it harder to weigh accurately. Calcium chloride dihydrate (CaCl₂·2H₂O, MW 147.01 g/mol) contains two moles of water per mole of salt, is more stable under typical lab conditions, and is the preferred form for most gravimetric solution preparation. Always confirm which form your protocol specifies before weighing to avoid concentration errors.

Can calcium chloride dihydrate be used for bacterial transformation?

Yes. Calcium chloride is the classic reagent for preparing chemically competent E. coli cells. Bacteria are incubated in cold CaCl₂ solution (typically 60–100 mM), which transiently permeabilises the outer membrane and allows plasmid DNA to enter cells during a brief heat shock at 42 °C. Reagent-grade or molecular-biology-grade CaCl₂·2H₂O (SKU C431167) is appropriate for this application; use freshly prepared, ice-cold solutions for best transformation efficiency.

Why does my calcium chloride dihydrate clump together in the bottle?

Clumping is caused by moisture absorption (hygroscopic caking). Even brief exposure to humid laboratory air allows the dihydrate crystals to absorb additional water, causing them to fuse into lumps. To prevent this, always reseal the container tightly immediately after use, store in a cool dry location, and consider transferring the reagent to a desiccator or airtight container with silica-gel desiccant after opening. Clumped material is still usable if it has not visibly liquefied, but weigh carefully and consider drying at 100–120 °C before use if gravimetric accuracy is critical — note that extended heating above ~30 °C begins to remove water of crystallisation.

Is calcium chloride dihydrate compatible with phosphate-buffered saline (PBS)?

Calcium ions react with phosphate ions to form insoluble calcium phosphate precipitates, so CaCl₂ is generally not directly added to standard PBS. If your protocol requires both calcium and a phosphate buffer, use a low-phosphate or phosphate-free buffer system, or add calcium at very low concentrations and check for visible precipitation. Alternatively, use HEPES- or Tris-based buffers as the primary vehicle when calcium must be present at physiological or higher concentrations.

What concentration of calcium chloride is typically used in mammalian cell culture media?

Most standard mammalian cell culture media (e.g., DMEM, MEM) contain calcium at approximately 1.8 mM, which is close to physiological extracellular calcium levels. When preparing media from powder or supplementing custom formulations, CaCl₂·2H₂O is added to achieve this concentration. Always use cell-culture-grade or equivalent tested reagent to avoid introducing endotoxin or heavy metal contaminants that could affect cell viability.

References

1. Sambrook J, Russell DW. Molecular Cloning: A Laboratory Manual, 3rd ed. Cold Spring Harbor Laboratory Press, 2001.
2. Freshney RI. Culture of Animal Cells: A Manual of Basic Technique and Specialized Applications, 6th ed. Wiley-Blackwell, 2010.
3. Aladdin Scientific Product Page: Calcium Chloride Dihydrate, SKU C431167 (Sigma ref C5080). https://www.aladdin-e.com

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.