Sciencemadness Discussion Board

Hygroscopy

User - 1-9-2009 at 00:57

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 :P


[Edited on 1-9-2009 by User]

User - 3-9-2009 at 12:09

Isnt there anyone who could give me an awnser?

Rich_Insane - 3-9-2009 at 12:44

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.

watson.fawkes - 3-9-2009 at 17:02

Quote: Originally posted by User  
Why is for example CaCl2 so attracted to water?
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.