"Michi Henning" wrote in message
...
Margolis" wrote in message
...
"Michi Henning" wrote in message
...

No, that's not correct. In fact, CO2 dissolves very readily in
water.


I have to disagree very strongly. co2 does not like to mix with water
at
all.

At room temperature, solubility of CO2 is 0.9 liters in one liter of
water.
So, given equal volumes of CO2 and water, almost all of the CO2 can
be dissolved in the water. Venous blood contains 50-60% CO2 by
volume. Most people would call that "readily dissolves" (and many
text books use precisely that phrase).

That is why it dissapates out of the water so rapidly if there is any
surface turbulance at all.

No, that is not why this is happening. The reason is that there is an
equilibrium at which the amount of CO2 that dissolves into the water
equals the amount of gas that outgasses from the water. The
concentration at which that equilibrium occurs is determined by the
partial pressure of CO2 in air. If water contains more CO2 than
the natural equilibrium, CO2 will gradually escape from the water
until the natural balance is restored. If you agitate the water
surface,
you increase the surface area at which water is in contact with air
and, as a result, CO2 escapes quicker than it would if the surface
were still. However, eventually, the exact same balance will be
established, whether you agitate the water or not.

That is also why co2 in water in nature is
around 2-3ppm while atmospheric concentrations are around 375ppm.

No, that's not the reason. The reason is that air only contains
around 0.0314% CO2. The amount of CO2 that dissolves in water
is limited by the partial pressure of CO2 in the air, not by the
solubility
of CO2 in water. If you put a 100% CO2 atmosphere above water,
you end up with the above mentioned 0.9 liters of CO2 per liter
of water.

One effect of the greenhouse gas problem is that, over the past
decades,
we have increased the CO2 levels in the atmosphere, meaning that more
CO2 dissolves into the oceans than was previously the case. Because CO2
forms carbonic acid in water, that causes a pH drop. That drop in pH
(among other things) has been linked to the increasing death of corals
in the Great Barrier Reef. Basically, all the extra CO2 we are
producing
readily dissolves into the oceans, raising the pH in the bargain.

In summary: CO2 *does* readily dissolve in water. If you want proof,
put a hose into your tank and pump CO2 into it. Watch each
CO2 bubble as it rises -- it gets visibly smaller as it makes its way
to the surface. The amount by which the bubble gets smaller is
the amount of CO2 that has dissolved into the water.

Cheers,

Michi.

--
Michi Henning Ph: +61 4 1118-2700
ZeroC, Inc. http://www.zeroc.com

Another way to look at this is, the rate at which a gas leaves (CO2
quickly outgassing) is indicative of how easily or slowly it enters.

Michi, can the same thing be said about O2, or are there additional
variables at work?

What is the equilibrium %s of O2 in water vs air?

Using the same 0.9 litre example above, how would O2 figure?

My understanding is that under normal circumstances, CO2 (injection) will
not crowd out O2. Using the litre saturation points, where would CO2 and
O2 level off if applied simultaneously?

--
www.NetMax.tk who loves the science of keeping fish happy : )