producing CO2 from vinegar and baking soda

[David Marshburn <marshbur at cs_unc.edu>]

So, I was reminded of the childhood sciencey toys or science kits where
vinegar and baking soda are combined to produce CO2 and am thinking about
how to use this reaction to inject CO2 into a planted tank.  

My thought is to drip vinegar slowly into a large, sealed reservoir of
baking soda (well, sealed save for a tube running to the tank).  This
avoids the problem of mixing all the baking soda and vinegar at once and
then storing the resulting CO2 (which is produced almost immediately by
the reaction).

Anyone done anything like this?  I don't seem to see anything in the APD
archives (but the searches seem to be partially broken, atm).

I suspect I'd need to calculate rates of CO2 production given vinegar
concentrations, which are usually 5% (I believe common household baking
soda is essentially pure NaCO3).  Attempting this on the back of the
envelope, and playing fast and loose with the appropriate quantities, one
drop from a 5%-by-volume solution of vinegar should introduce enough
acetic acid to produce a drop of liquid CO2 (ignoring that such a thing
doesn't exist) 1/20 the size.  However, as a gas, the CO2 is
considerably less dense than water (e.g. vinegar), and the resulting
volume of CO2 should be on the order of a few times the size of the drop
of vingar (I can't lay my hands on even approximate numbers for this).
So, I'll proceed with the idea that a drop of vinegar onto baking soda
will produce a few pea-sized bubbles of CO2 (and this is easily testible).

Can anyone give a figure for how much CO2 is a good rate in terms of,
say, mass or volume at room temperature and pressure?

Seems like a cheap needle valve from a hardware store would do to control
the drip of vinegar reliably, and that I wouldn't need to worry about
dumping and such things since the vinegar isn't under pressure.  One
concern, I think, would be how well the vinegar and baking soda would mix
once everything is mostly wet.

(this may not be any better than a yeast-based DIY CO2 system, but it
strikes my fancy at the time to try it out and see how it works!  I'd be
very pleased to hear, though, if anyone's tried it before I start
experimenting :).


btw, can anyone confirm if the following is really an SAE or not?  Most
of the signs look correct from all the descriptions I've read, but the
color seems a bit wrong, and the stripe doesn't seem to go quite all the
way through the tail....  The fish store said it was an "algae-eating
shark" and not an SAE, but all the characteristics point to SAE...
http://www.cs.unc.edu/~marshbur/2002-11-01-aquarium/aquarium%20004.jpg

cheers,
-david