User
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Hygroscopy
Good morning.
Last night I was wondering about something.
First of all iam quite familiar with the term hygroscopy as in practical use and when these bondings occur. Or the molecules/ions that just like water
without binding to it etc etc.
Then arose my question(s).
Why is for example CaCl2 so attracted to water?
Why do certain substances even have this behaviour?
Also how is it explained that CaCl2 does attract water ( even binds it to itself) and sodium chloride does not.
Well what i do know  is that certain metals often do this.
I know a lot of questions
I hope someone can offer me a decent story 
[Edited on 1-9-2009 by User]
What a fine day for chemistry this is.
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User
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Isnt there anyone who could give me an awnser?
What a fine day for chemistry this is.
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Rich_Insane
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Many hygroscopic compounds are hygroscopic because they form hydrates with water. Basically the water may just pass by an anhydrous crystal of CaCl2,
and the CaCl2 will take it in. It just forms hydrate crystals.
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watson.fawkes
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I might suggest starting by looking up the energy of the
reaction CaCl2 + n H2O --> CaCl2.n(H2O), that is, the energy associated with the hydration of an anhydrous species.
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