Learn more physics!
I will like to know, if 97% of the earths water is salty and its recycled, why isnt the rain salty?
- Noah (age 8)
Ojus Elementary, North Miami, FL
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.
(republished on 07/24/06)
Follow-up on this answer.