Hi Amy,
We're not sure if you're asking about separate oxygen molecules
dissolved in water or the oxygen which is part of each water molecule.
Most water you find around, in the ocean, lakes, streams, and even
coming out of the tap, has air dissolved in it. Air is about 20%
oxygen, and so yes, there is dissolved oxygen in the water. This
dissolved oxygen is what fish need to respirate, otherwise they would
suffocate. So you can say that the water gives off oxygen.
Tap water sometimes gets more air dissolved in it than would be in
equilibrium if you just let it sit still in a jar. If you put tap water
in a glass or a jar and let it stand for a while, some of the dissolved
air will bubble out. When I was small, we always did this before
putting the water in the fishtank, to keep bubbles from forming in the
fish's gills.
Water is composed of molecules containing hydrogen and oxygen
atoms. These don't come apart on their own, however. You can break
water molecules up by the process of electrolysis. Passing an
electrical current through the water will cause oxygen to bubble up on
one electrode and hydrogen on the other. The process can go more easily
if some acid is added to the water. Electrolysis of water is dangerous!
The hydrogen is extremely flammable and can explode.
Tom (w mike)
(published on 10/22/2007)
