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CO2 Production using baking soda

  1. Aug 10, 2010 #1
    So, I'm making a non-yeast based co2 reactor for my fish tank, and currently the idea has come down to baking soda, an acid, and a iv drip line to control the rate of the reaction.

    My first question, is what is the best acid to use that will produce stable, non harmful salts as byproducts with co2.

    First idea was vinegar (acetic acid). I calculated that for 7.5g of baking soda, I'd need 180ml vinegar (5% acetic acid) to keep a 29 gallon tank at 30ppm co2 (ppm is mg/L), and there is just too much water. Next I went to muriatic acid (HCL at around 30%) Possible problems with this are that it is possibly dangerous to handle and I'm not sure how the plastic will hold up. Muriatic acid is easy to find, but how hard is it to find other acids like a stronger acetic acid? Also for byproducts, sodium acetate is fun to play with, and I'm assuming not that harmful, but with HCL you can CaCl2, which appears harmless (another salt)

    My second question is kind of complicated, with many variables. It is about outgassing of co2 and keeping the tank at 30ppm. If I dose the tank, and the level is at 30ppm, let's assume the tank is at 80 degrees Fahrenheit and there are maybe 1/3" ripples on the top of the tank. How much co2 will be outgassed ( I guess we can add STP here). I'm not really sure what variables I'll need to give to calculate this, so I'll try to make them up as I go along.


    TIA
     
  2. jcsd
  3. Aug 10, 2010 #2

    Borek

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    Staff: Mentor

    I would go for muriatic acid, with acetic reaction would be way too slow.

    As for degassing - it is probably easier to check experimentally than to calculate.

    --
     
  4. Aug 10, 2010 #3
    Thanks for the quick reply

    The closest thing I have to testing co2 levels is a pH indicator (bromothymol blue I think) and a 4dKH reference solution, so when the solution is green, then the co2 levels are between 20-40ppm I think.

    As for degassing, I guess it would be pretty hard to calculate, as there are too many unknown variables.

    I'm also wondering if there will be a way to get rid of the excess water? I was thinking of using a sponge or something absorbent. I guess it's not a big deal, as baking soda is cheap, and I think muriatic acid is as well, but the purpose of this was to reduce the amount of maintenance work needed compared to the yeast-sugar method. I'm guessing I'll need between 30-60mL of muriatic acid a day, which will be around 70% water. I guess this isn't that much water, but I'm trying to plan on the container now. Will the water more likely be absorbed into the baking soda or will it probably evaporate?

    Thinking back to high school chemistry, will I have a problem with heat? I remember the vinegar-baking soda reaction creates some heat, but HCL is much stronger, and in a much greater (around 6x) greater concentration.

    I'm planning on using some sort of glass container for the "reactor" now, but will the HCL be reactive towards airline tubing and an IV bag? I'm thinking of using something like this to control the drip rate

    iv-drip-largethumb6985087.jpg
     
  5. Aug 10, 2010 #4

    Borek

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    Staff: Mentor

    Presence of water doesn't matter much - it won't stop the reaction, you will just have not a solid baking soda, but something looking like a wet sand.

    Amount of heat should be negligible, reaction mixture will easily cool down by itself (assuming container is not specially isolated from the surroundings).

    I would use slightly diluted acid (so for example not 38% as usually sold, but mixed with equal volume of water - just remember to add acid to water, not water to acid), otherwise HCl (which is volatile) could easily enter aquarium together with carbon dioxide.

    Perhaps you can try to pass the gas through another tube filled with carbonate to be sure HCl was absorbed?

    Reactivity of tubing... most plastics should survive if the acid is not highly concentrated, but the simplest answer is - check.
     
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