Calcium chloride hexahydrate melts

Calcium(II) chloride hexahydrate melts, supercooling phenomenon, 39 430, 432 Calcium(II) chloride hydrate, melt, 39 426-432... 

Limestone (CaC03) is treated with hydrochloric acid and water to manufacture calcium chloride hexahydrate. This compound is used to melt ice and snow on pavements and roads. 

Feilchenfeld H, Fuchs J, Sang S (1985) The melting point adjustment of calcium chloride hexahydrate by addition of potassium chloride or calcium bromide hexahydrate. Sol Energy 34 199-201... 

White crystal, powder or flake highly hygroscopic the compound and its solutions absorb moisture from the air at various rates depending on calcium chloride concentrations, relative humidity and vapor pressure of water in the air, temperature, surface area of exposed material, and the rate of air circulation at 40% and 95% relative humidity and 25°C, one gram anhydrous calcium chloride may absorb about 1.4 g and 17 g water, respectively. (Shearer, W. L. 1978. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., vol. 4, pp. 432-6. New York Wiley Interscience) density 2.15, 2.24, 1.85, 1.83 and 1.71 g/cm for the anhydrous salt and its mono-, di-, tetra- and hexahy-drates, respectively anhydrous salts melts at 772°C, while the mono-, di-, tetra- and hexahydrates decompose at 260°, 175°, 45.5° and 30°C, respectively the anhydrous salt vaporizes at 1,935°C highly soluble in water, moderate to high solubility in alcohol. 

Note that the molar enthalpies of melting of the salt hydrates are generally rather larger than those of similar anhydrous salts melting at a much higher temperature. Compare, for instance the Am///kJ moF of lithium salt trihydrates with the anhydrous salts nitrate 36.4 vs. 26.7 and perchlorate 40.6 vs. 17.0, the sodium salt decahydrates with the anhydrous salts carbonate 72.0 vs. 30.0, sulfate 78.7 vs. 23.0, and the calcium salt hexahydrates with the anhydrous salts chloride 37.2 vs. 28.5, bromide 35.6 vs. 28.9. 

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