Now THAT is odd (electric, box, chemistry, physics)
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Just tried to make a batch of carbon dioxide for use in making carbonated water. We all know that baking soda is used in fire extinguishers because it generates CO2, right? Online, I found that baking soda in water will give up the CO2 starting when heated to about 120, and effectively finishing when heated to boiling.
So... I sealed a tube to a jar lid. Filled the jar with 4 oz of baking soda and 12 oz of water, stuck it in a double boiler, with a garbage bag at the end of the tube to collect the CO2.
The solution started bubbling when heated. I mean SERIOUSLY bubbling. But the bag collected almost NO CO2. Took the bag off, stuck my finger over the end of the tube. No pressure. Wrapped electrical tape around the lid and top of bottle. STILL no pressure - even though the solution was bubbling furiously.
Funnier than H. A reminder to me to never assume.
Go ahead. Try it yourself. Makes a neat parlor trick to have a solution bubble furiously and not build up pressure in a closed container. Yeah, I was making carbonates out of bicarbonate. The base was counteracting the carbonic acid.
If you really want the CO2 you could use a vacuum to pull off the gas. Even a small pressure is enough to keep the CO2 in solution. That is why pop doesn't go flat when it gets warm if the cap is on.
I didn't realize that H2O with baking soda (sodium bicarbonate) would release CO2 without some acid present (vinegar for example). I do know that sodium cabonate (baking powder) will do that in plain H2O though.
Never the less:
I believe (as I think Chemistry Guy was getting at) the explanation is the physics/chemistry of the partial pressure gas laws.
Actually, the gas pressure laws don't seem to be the major factor here.
When CO2 is "dissolved" (bad word, I know) in water, it forms a mild acid. When there is baking soda in water it is alkaline. The two (loosely speaking) cancel each other out. Using a vacuum to get the CO2 out prior to it recombining would likely lower the boiling point of water enough to present another problem.
Time for me to see what happens with another undocumented technique. I refuse to pay a buck for two liters of water and some bubbles, and I want to avoid buying a big CO2 tank.
or how about order some online frozen food such crab cakes etc. They get shipped in a styrofoam box along with a good size chunk of dry ice. Put water and a chunk (size TBD) into a pressure vessel(s) and close the valve.
???
Give me a call...I"ll help you finish off the crab cakes
What I was hinting at was that the equilibrium of a reaction that produces a gas as a product can be forced to the left by increasing the pressure or pulled to the right by applying a vacuum. I am not sure what you are trying to do chemically, but if you haven't already tried it, adding acid will violently increase the rate of CO2 formation, ala the ubiquitous vinegar and baking soda volcano. However, you will need to compress the CO2 considerably if you want to carbonate soda with it, as soda typically is very acidic and requires a lot of 'pushing' to carbonate. In the great scheme of things, I think carbonation using compressed gas cylinders is about as efficient as it gets short of a fermentation process.
A CO2 tank made for paintball guns will cost you less than $15, and some places even refill them for free. Dry ice is even cheaper, but it is difficult to store for more than a few days. If you are really ambitious you can make your own dry ice using the compressor from an old fridge and some plumbing supplies. I like chemical solutions to problems as much as anyone, but when you buy common chemicals you are really paying a premium for the packaging, storage, and logistics more so than the substance itself, and it is a lot cheaper to transport and store CO2 than any solid substance.
I was thinking once you get a chunk of dry ice you take your stash of empty 2 liter soda bottles, break up the dry ice into appropriate sized pieces,load up the bottles one at a time with the proper amount of dry ice (by weight ?), then add the water and cap off and set aside for awhile. Continue loading bottles until you've used up your recently acquired chunk of dry ice.
Not sure what the bursting pressure of a typical soda bottle is but I'd experimentally work up to a given amount of dry ice.
How simple things can go bad:
At work a cpl of us filled a typical Nalgene reagent type bottle with liquid nitrogen, capped it of and watched it spray out the little angled discharge tube.
BAD idea. The little discharge tube somehow became plugged , the plastic got brittle, and the resulting sound and explosion was very impressive. Fortunately the only thing damaged was the under shorts of some folks standing around .
BTW...a CO2 fire extinguisher could work....don't know what they get for a recharge.
Last edited by JBrown; 07-27-2011 at 07:23 PM..
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The little discharge tube somehow became plugged , the plastic got brittle, and the resulting sound and explosion was very impressive. Fortunately the only thing damaged was the under shorts of some folks standing around . 
