Calcium chloride: Difference between revisions

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==Abstract==
==Abstract==


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


==Hydrate stages==
==Hydrate stages==


[[Sinjarite]]: CaCl<sub>2</sub>•2H<sub>2</sub>O <br> [[Calcium chloride tetrahydrate]]: CaCl<sub>2</sub>•4H<sub>2</sub>O <br> [[Antarcticite]]: CaCl<sub>2</sub>•6H<sub>2</sub>O
[[Calcium chloride monohydrate]]: CaCl<sub>2</sub>•H<sub>2</sub>O <br> [[Sinjarite]]: CaCl<sub>2</sub>•2H<sub>2</sub>O <br> [[Calcium chloride tetrahydrate]]: CaCl<sub>2</sub>•4H<sub>2</sub>O <br> [[Antarcticite]]: CaCl<sub>2</sub>•6H<sub>2</sub>O


==Solubility==
==Solubility==
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[[file:D CaCl2e.jpg|thumb|left|800px|Figure 2: Deliquescence behaviour of calcium chloride in the temperature range from -45 to 80 °C. The water activity ''a<sub>w</sub>'' is plotted against the temperature.]]
[[file:D CaCl2 e.jpg|thumb|left|800px|Figure 2: Deliquescence behaviour of calcium chloride in the temperature range from -45 to 80 °C. The water activity ''a<sub>w</sub>'' is plotted against the temperature.]]
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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.
The hydration/dehydration and crystallization/deliquescence processes in the CaCl<sub>2</sub>-H<sub>2</sub>O system can occur by either changing relative humidity or temperature. The deliquescence relative humidity decreases with increasing temperature. At room temperature (20ºC), the hexahydrate [Antarcticite]] is the stable phase, having a deliquescence humidity of about 30% RH. Lowering the relative humidity at the same temperature, calcium chloride tetrahydrate forms at values below 18% RH, while dehydration to the dihydrate ([[sinjarite]]) occurs at 9% RH, while the latter changes to the monohydrate at 6% RH.
 
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{|border="2" cellspacing="0" cellpadding="4" width="30%" align="left" class="wikitable"
|+''Table 1: Deliquescence and equilibrium humidities at 20 °C.''                   
|-
|bgcolor = "#F0F0F0" align=center| '''Phase transition'''
|bgcolor = "#F0F0F0" align=center| '''Deliquescence or equilibrium humidity at 20°C'''
|-
|bgcolor = "#FFFFEO" align=center| [[Antarcticite]]-solution
|bgcolor = "#FFFFEO" align=center| 33.3 %
|-
|bgcolor = "#FFFFEO" align=center| [[Antarcticite]]-[[Calcium chloride tetrahydrate]]
|bgcolor = "#FFFFEO" align=center| 18.5 %
|-
|bgcolor = "#FFFFEO" align=center| [[Calcium chloride tetrahydrate]]-[[Sinjarite]]
|bgcolor = "#FFFFEO" align=center| 9 %
|-
|bgcolor = "#FFFFEO" align=center| [[Sinjarite]]-[[Calcium chloride monohydrate]]
|bgcolor = "#FFFFEO" align=center| 6 %
|}
<br clear="all">


==References==
==References==
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[[Category:Stahlbuhk,Amelie]][[Category:Calcium chloride]] [[Category:Chloride]] [[Category:R-MSteiger]] [[Category:InReview]] [[Category:Salt]]
[[Category:Stahlbuhk,Amelie]][[Category:Calcium chloride]] [[Category:Chloride]] [[Category:R-MSteiger]] [[Category:editing]] [[Category:Salt]]

Latest revision as of 21:25, 30 August 2016

Author: Amelie Stahlbuhk
back to Chloride


Abstract[edit]

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

Hydrate stages[edit]

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

Solubility[edit]

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[edit]

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


The hydration/dehydration and crystallization/deliquescence processes in the CaCl2-H2O system can occur by either changing relative humidity or temperature. The deliquescence relative humidity decreases with increasing temperature. At room temperature (20ºC), the hexahydrate [Antarcticite]] is the stable phase, having a deliquescence humidity of about 30% RH. Lowering the relative humidity at the same temperature, calcium chloride tetrahydrate forms at values below 18% RH, while dehydration to the dihydrate (sinjarite) occurs at 9% RH, while the latter changes to the monohydrate at 6% RH.


Table 1: Deliquescence and equilibrium humidities at 20 °C.
Phase transition Deliquescence or equilibrium humidity at 20°C
Antarcticite-solution 33.3 %
Antarcticite-Calcium chloride tetrahydrate 18.5 %
Calcium chloride tetrahydrate-Sinjarite 9 %
Sinjarite-Calcium chloride monohydrate 6 %


References[edit]

Literature[edit]

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

A phase is a physically distinctive form of matter and is characterized by having relatively uniform chemical and physical properties.

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