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oups.com...
Jeff Rigby wrote:

Not that weak. If you take a distilled water and left it open pH
goes
down from 7 to about 5.7 - just because of the presence of dissolved
carbon dioxide.

PH changes from 7, in other words from 5-9 in distilled water take
very
little acid or base, in other words it's a very weak acid or base.

Remember that this change takes place in the presence of only about 380
ppmv of CO2 in the air. Increase amount of CO2 in the atmosphere and
the change will be higher. That doesn't mean carbonic acid is not a
weak one, you just don't need a strong acid to change pH when you have
solution close to pH 7.

That's like saying water is a solvent and it dissolves most compounds
because the hydrogen and oxygen molecule's geometry lends itself to
tearing
apart most compounds. We should be concerned with water too. In fact
it's
not the carbon dioxide that creates the acid, it's water. Without water
carbon dioxide is not an acid.

Water dissociates creating the same amounts of H+ and OH- ions. First
are connected with solution acidity, the latter with solution basicity.
Thus water is acidic and basic - to the same extent - at the same time.
That's why pure water is neutral.

I understood that water does NOT disassociate, it's a very stable and strong
bond, EXTREMELY strong bond, it's equalibrium reaction has very few
disassocited ions. It's geometry, were oxygen and hydorgen atoms are placed
in the molecule allow the water moleule to have a strong charge at each end
where the oxygen has a - charge and the Hydrogen has + charge. It ionizes
molecules because of this GEOMETRY not because water disassociates. It's
because of this geometry that water has unique properties when frozen. Cold
water sinks but ice floats!.

Pure water can not carry a charge! Try for yourself, put two electrodes in
distilled water and try to run a current thru water, you won't get one
untill you introduce a compound that can be ionized to carry the current.
If pure water can not carry a charge then it is not disassociated. You can
crack the water molecule with enough voltage but it doesn't ionize it cracks
and releases hydrogen gas and oxygen gas.