Calcium Chloride
Properties
| State | Solid (white, highly hygroscopic granules or flakes) |
| Color | White |
| Solubility | Highly soluble in water (745 g/L at 20°C; dissolution is exothermic) |
| Melting Point | 772°C |
| Boiling Point | 1935°C |
About Calcium Chloride
Calcium chloride is the salt that does interesting thermodynamic work whenever it touches water. ΔHsoln is around −82 kJ/mol for the anhydrous form — strongly exothermic — and the equilibrium freezing point of a saturated brine sits near −51 °C, which is why CaCl2 keeps deicing pavement long after sodium chloride has given up at −21 °C. The combination of large negative dissolution enthalpy and dramatic freezing-point depression also explains its dual role as a hygroscopic desiccant and a self-heating ingredient in MRE-style food warmers. The Ca²⁺ ion is small (1.00 Å, six-coordinate) and hard, with two empty coordination sites in the anhydrous lattice; that is why anhydrous CaCl2 will pull water out of an organic solvent or pull moisture out of humid air until it deliquesces into a brine. In the lab and the brewery, the same Ca²⁺ ion bridges casein micelles in milk to firm cheese curd, neutralizes the phosphate backbone of plasmid DNA in heat-shock transformation of E. coli, and accelerates Portland cement hydration by promoting C3S setting. As an E509 food additive it firms canned tomatoes (cross-linking pectin) and forms the gel skin in spherification, where alginate-bearing droplets hit a CaCl2 bath and crosslink instantly via egg-box junctions.
Where you'll encounter it
If you've worked in a molecular biology lab you've used CaCl2 to make competent E. coli; if you've made cheese you've added it to pasteurized milk at about 0.02% to firm the curd. In a chocolate kitchen running modernist cuisine, CaCl2 baths turn alginate-laced juices into the famous yolk-like spheres in 30 seconds flat. On a winter road maintenance crew, the brown stains on the asphalt after a snowstorm are CaCl2 brine, sprayed because it works at temperatures where rock salt is just expensive gravel. Concrete crews mix it into cold-weather pours as a set accelerator at 1–2% of cement weight. Around any oil rig you'll find drums of CaCl2 brine used as a clear, weighted completion fluid that won't damage the producing formation.
Common Uses
- Winter de-icing brine effective down to about −29 °C, well past NaCl's limit
- Drying agent for hydrocarbons and aprotic solvents (not alcohols or amines, which form adducts)
- Calcium source in heat-shock transformation of chemically competent E. coli
- Firming agent for canned tomatoes and the alginate gel in spherification (E509)
- Set accelerator in cold-weather Portland cement pours at 1–2% of cement mass
- Clear brine completion fluid in oil and gas wells at densities up to 11.6 lb/gal
- Dust suppressant on unpaved haul roads via deliquescent moisture retention
- Calcium standard for hardness assays and AAS calibration after careful drying
Safety Information
GHS H319 — causes serious eye irritation. Dust and concentrated solutions desiccate skin; chronic exposure causes dermatitis. Exothermic dissolution can heat a poorly designed mixing tank past 60 °C, scalding operators if added too fast. Oral LD50 (rat) about 1.0 g/kg, low concern at food-additive doses. Reacts with zinc to slowly evolve hydrogen — keep brine away from galvanized hardware. OSHA does not list a specific PEL; treat as nuisance dust at 15 mg/m³ total.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.