Calcium chloride

Author: Amelie Stahlbuhk
back to Chloride

Abstract

The different hydrate stages of calcium chloride are presented, as well as their behavior regarding solubility and hygroscopicity.

Hydrate stages

Sinjarite: CaCl₂•2H₂O
Calcium chloride tetrahydrate: CaCl₂•4H₂O
Antarcticite: CaCl₂•6H₂O

Solubility

Figure 1: Solubility of calcium chloride in water. The molality m [n(CaCl₂•xH₂O)•kg(H₂O)^-1] is plotted against the temperature.

Under standard conditions the hexahydrate of calcium chloride Antarcticite is the stable form. The salt has got a high solubility in water which increases with increasing temperatures. The dehydration steps to the calcium chloride tetrahydrate and to sinjarite take place at temperatures of 30 °C and 45 °C, respectively.

Hygroscopicity

Figure 2: Deliquescence behaviour of calcium chloride in the temperature range from -45 to 80 °C. The water activity a_w is plotted against the temperature.

At room temperature the present phase Antarcticite has got a deliquescence humidity of about 30 %. The deliquescence behavior depends on the temperature as the deliquescence humidity decreases with increasing temperature. Changing the relative humidity at 20 °C, calcium chloride tetrahydrate forms at values below 18 % RH. The dehydration to the Dihydrate (sinjarite) and the monohydrate occurs at 9 % RH and 6 % RH, respectively.

concentration given as amount of substance (mol) of the dissolved substance per kilogram solvent; unit: mol•kg-1.

the relative humidity, above which a material, e.g. a salt, absorbes humidity from the air and dissolves.

relative humidity