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. There is no substance-specific airborne limit; treat the dust as a nuisance particulate.
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. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.