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Homework Help: Calculation of dissolved total inorganic carbon

  1. Feb 8, 2007 #1
    1. The problem statement, all variables and given/known data

    I'm trying to calculate Total Inorganic Carbon (TIC) for an experiment in which I have measured pH and Headspace CO2 concentration (%v/v). Approximate values are:

    pH 7.3
    Headspace CO2 2.5 %v/v

    2. Relevant equations



    3. The attempt at a solution
    I've tried two approaches:

    Firstly I used the CO2 concentration and Henry's law constant to estimate the dissolved CO2 concentration, and then combined this with the headspace concentration to get total concentration.

    Secondly, I have tried a more elaborate method, which takes account of dissolution of CO2 in water to H2CO3, HCO3- and CO32-, and uses the partial pressure of CO2 in the heaspace, the equilbrium constants for each reaction and the pH to calculate TIC.

    I get two completely differenet answers, and I have no idea which one is correct.

    Method 1 gives dissolved concentration that is similar to the headspace concentration, whereas method 2 gives a dissolved concentration that is approximately 10 times greater than the headspace concentration. Any thoughts on which is the correct method, and what kind of ball park figures I should expect??
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
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