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Q & A: evaporation and salt

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Most recent answer: 10/22/2007
Q:
why does the salt stay behind when saltwater evaporates?
- elaina (age 14)
ny
A:
The dissolved salt consists of electrically charged particles (ions), Na+and Cl-. It takes a lot of energy to remove a charged particle from water and put it in gas. So the charged particles stay stuck in the liquid. The reason they have lower energy in the liquid is that water has molecules with charged parts, and they arrange themselves to reduce the electrical energy of the ions. Now you might wonder why a Na+and a Cl- don't stick together to make a neutral (no-charge) molecule, which could evaporate more easily. I'm not sure exactly, but dry NaCl doesn't consist of separate molecules but rather one big crystal of alternating Na+and Cl-. So I guess neutral NaCl molecules arenít very stable, for reasons connected with detailed quantum mechanical states.

Mike W.

Lee H

(published on 10/22/2007)

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