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Name: Rachel
Status: student
Grade: 6-8
Location: NJ
Country: USA
Date: Fall 2011


Question:
When the water in the salt and water solution evaporates, why were the salt crystals in square form? And why did they have X's on them? Or did I just see wrong?



Replies:
The most stable form of NaCl at 298 K and 1 atm is a cubic form. So the answer to "why" that is the case requires much more complicated calculation. That does not mean that some other arrangement is not more stable at lower temperatures and/or higher pressures. It is just that we do not commonly do those experiments. Sometimes for clarity X and O (or other symbols) are used instead of the atomic symbol for the element -- that is no big deal.

Vince Calder


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