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Name: Devon
Status: other
Grade: other
Location: MI
Country: N/A
Date: December 2006


Question:
Does the crystal geometry of the hygroscopic compound change between its anhydrous and hydrate forms? If so, how could one tell how they would differ?



Replies:
Devon, The crystal form of an anhydrous form and a hydrated form must change, because the crystal lattice must accommodate water molecules. The reason that hygroscopic (thank you for not typing hydroscopic;) molecules pick up water is to lower the crystal energy. Typically one tells the difference by using X-ray diffraction. http://en.wikipedia.org/wiki/X-ray_diffraction The link above is included for a more in-depth article on X-ray diffraction.

Matt Voss


Yes, it changes. You cannot predict how very easily, but you can look up the crystal structures the two forms have in scientific reference literature.

Whether you can see the transformation by eye is another matter which I have no experience with. It might not be real clear.

Jim Swenson


The crystal structure of an anhydrous salt and its (one or more) hydrates are not related in a simple form. One factor is how water molecules can "pack" within the crystal structure, but just how this occurs cannot be determined by any simple model that I am aware of.

Vince Calder



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