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Thread: Carbon Dioxide level

  1. #1 Carbon Dioxide level 
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    Ok, here is my question:

    I have a fish tank - it contains nothing but water.

    I bubble carbon dioxide into the fish tank at a set rate and measure the CO2 concentration at a set location; let's say it reads 20 mg/L.

    The water is at 25C.

    Now I raise the water temperature to 30C but change nothing else.

    The water still measures 20 mg/L....right???

    The solubility of CO2 in water at 25C is some 1450mg/L, and it's somewhere in this vicinity at 30C too.

    Because in my experiment above I am nowhere near the saturation "line" (if I were to graph the solubility), I expect that the concentration of CO2 in the water will be exactly the same.

    Agree?

    If not, why not. :-)

    Scott.


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  3. #2  
    Reptile Dysfunction drowsy turtle's Avatar
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    At a higher temperature, carbon dioxide will evaporate out of the water at a greater rate.


    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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  4. #3  
    Forum Freshman Robinol's Avatar
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    At higher temperature, volume will also increase and concentration of CO2 will decrease.
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  5. #4  
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    Quote Originally Posted by drowsy turtle View Post
    At a higher temperature, carbon dioxide will evaporate out of the water at a greater rate.
    I was under the impression that the rate the CO2 left the water was in relation to partial pressure? The partial pressure is the same though....
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  6. #5  
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    Quote Originally Posted by Robinol View Post
    At higher temperature, volume will also increase and concentration of CO2 will decrease.
    Volume of what?
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  7. #6  
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    Given that the solubility of permanent gases decrease with increasing temperature why in the world wouldn’t partial pressure have to increase if you wanted the dissolved gasses to remain the same?

    When the temperature of the system changes Henry’s constant (probably should be called coeffiecient) changes.

    Another way of saying it is for the gas to remain the same at higher temperatures then the partial pressure would have to increase

    If you do not like it you will have to take it up with Henry
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  8. #7  
    Forum Freshman Robinol's Avatar
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    Quote Originally Posted by bobfloyd View Post
    Quote Originally Posted by Robinol View Post
    At higher temperature, volume will also increase and concentration of CO2 will decrease.
    Volume of what?
    When heat is given to the system the volume of water will increase and will cause it to expand. Is that what you wanted to ask?
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