Salt-free Rain Water
Most recent answer: 10/22/2007
Q:
I will like to know, if 97% of the earths water is salty and its recycled, why isnt the rain salty?
Thank You.
- Noah (age 8)
Ojus Elementary, North Miami, FL
- Noah (age 8)
Ojus Elementary, North Miami, FL
A:
The rain water comes from water vapor that has gone into the
atmosphere, mostly from oceans. Vapor means molecules that are
bouncing around in mostly empty space without spending much time in
contact, unlike a liquid where they stick together. When the vapor
cools enough, it condenses into liquid water that falls as rain.
So why does the water vapor lack salt? Dissolved salt consists of ions- electrically charged versions of atoms. In liquid water, the electrically charged parts of the water molecules arrange so that on average their positive parts are near the negative ions, and the negative parts nearer the positive ions. That greatly lowers the energy of the ions, compared to the energy they would have off on their own. In other words, the ions stick to the liquid water. They actually stick to it much better than the water molecules do. So water molecules evaporate off into vapor, leaving the salt behind.
Mike W.
So why does the water vapor lack salt? Dissolved salt consists of ions- electrically charged versions of atoms. In liquid water, the electrically charged parts of the water molecules arrange so that on average their positive parts are near the negative ions, and the negative parts nearer the positive ions. That greatly lowers the energy of the ions, compared to the energy they would have off on their own. In other words, the ions stick to the liquid water. They actually stick to it much better than the water molecules do. So water molecules evaporate off into vapor, leaving the salt behind.
Mike W.
(published on 10/22/2007)