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, any Antarcticite present has got a deliquescence humidity of about 30 %. It is also stable up to 30 °C at very low relative humidities, a fact that shows the hygroscopicity of the phase. At room temperature changes in the relative humidity do not provoke phase transitions. Calcium chloride tetrahydrate and Sinjarite have constant deliquescence humidities below 22 % in their temperature ranges.

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.