[nappy]

 Hi everybody,

This is my first post and I'm very happy to be here. I have had chemistry as a hobby since I was a little kid, even had a couple of mishaps with it but still love it.

My question is this easy (?)

I'm trying to make a "slow" CO2 generator using the following:

NaHcO3 + CH3COOH , which releases  CO2 + H2O + CH3COONa.

So far the reaction is OK using table vinegar and baking soda. The thing is I'm trying to make the reaction as slow as possible, in order to bubble the CO2 in a fishtank full of plants which need it to thrive.
Is there any way I can either dissolve the ingredients or use come kind of catalyst to make the reaction slower?

[Borek]

I would look for a way of slowly adding the acid, this is a rather fast reaction.

I am not convinced what you are doing will work the way you want it. Does the produced gas smell of vinegar?

[nappy]

Well it smells a little, but then again I can bubble it through some kind of solution that will absorb the smell, probably a baking soda solution will work well as a trap.

[Borek]

Only till it reaches an equilibrium, after that acetic acid will just pass though.

[nappy]

I've been thinking about the original question and haven't found an answer to it.

Should I dissolve the initial baking soda in water? And the vinegar as well? My thinking is that by dissolving the two main components in water it will actually reduce the speed of the reaction. Am I wrong?

The smell on the gas doesn't really matter because I would actually set the slow dosage of vinegar to produce CO2 during the time the plants in the aquarium have the lights on, which is approximately 6 to 7 hours and I don't think in that period the trap will saturate enough to let the smell of the vinegar pass. In any case, the trap would be changed daily, to start the next day with a fresh trap.

[Borek]

Should I dissolve the initial baking soda in water? And the vinegar as well? My thinking is that by dissolving the two main components in water it will actually reduce the speed of the reaction. Am I wrong?

In general yes, the lower the concentration the slower the reaction. However, if it will mean you need a several gallon tank for CO₂ production, it stops making sense, doesn't it?

In any case, the trap would be changed daily, to start the next day with a fresh trap.

Can be doable, just means more maintenance.

[nappy]

OK let's see... This is the setup I'll be using:

1.- A 2 Liter Cocacola bottle (it's the strongest out there because of the shapes it has) with dissolved baking soda, let's say with 200 grams of baking soda dissolved in water until the solution is clear, not to have any deposits on the bottom, to be able to see how far the acetate has been produced.

2- A 350ml PET bottle of dissolved acetic acid. I wouldn't know the concentration here, but it doesn't sound that difficult to figure out. This would be my acid deposit with a drop counter. It would have a hose at the bottom and the cap have a hole in it so air can get in for air to get in and allow the drops to fall.

3.- The PET bottle will feed the 2 Liter bottle slowly, thus releasing acid on the baking soda solution, producing CO2 and precipitating acetate on the bottom.

4.- The Cocacola bottle should have 2 holes on the cap to let the acid in and to let the CO2 out to the trap.

5- As mentioned in my last post, the trap would be changed daily if necessary, to avoid acetic acid gas to reach the fish. Also, two holes on the cap, 350ml bottle to bubble the CO2 and finally let the CO2 out inside the filtered water hose inlet at the top of the fishtank.

6- All of this connected with the necessary IV administration supplies.

How does that sound?

[Borek]

let's say with 200 grams of baking soda dissolved in water until the solution is clear, not to have any deposits on the bottom, to be able to see how far the acetate has been produced.

Sodium acetate is quite soluble, why do you expect it to precipitate out of the solution?

A 350ml PET bottle of dissolved acetic acid. I wouldn't know the concentration here, but it doesn't sound that difficult to figure out. This would be my acid deposit with a drop counter. It would have a hose at the bottom and the cap have a hole in it so air can get in for air to get in and allow the drops to fall.

You will have to keep it higher than the rest, as the produced carbon dioxide will increase the pressure in the first bottle.

How does that sound?

More or less doable, I am just not sure if practical.

[nappy]

Ummm...
Ok the baking soda dissolved in water is also to prevent me from shaking the big bottle frequently; second, yes the acetate is quite hygroscopic. In fact they use it to make freezing solutions I do have some of it somewhere in my refrigerator. So you think it's not necessary to dissolve the baking soda? wouldn't it get all clustered after the reaction?

I Just did the experiment both with dry and dissolved baking soda and my conclusion is that the baking soda dissolved works better at slowing the reaction, and it doesn't get clustered when used dry. The dissolved baking soda will need a big bottle (which I have ) to receive the acid. 

Let me tell you why I'm making this project:
The usual method of producing CO2 is to use sugar, yeast, water and a pinch of baking soda. If mixed properly, there will be a steady, nevertheless unstopable production of CO2 for about 4+ weeks. The main drawback is not being able to stop it at night which is the time at which plants do not need CO2. Another drawback is that you need at least 4  2 liter bottles for my fishtank (very bulky and hard to conceal underneath). I have used it, but it is a little more expensive, and the yeast spoils very quickly where I live (88% humidity), which is a problem since they don't sell little amounts but rather kilos or pounds. On the other hand, vinegar and baking soda will not spoil under humidity.