You have a sealed 2 liter flask that contains nothing but water and carbon dioxide. The flask is half-filled with liquid water, has a temperature of 25°c, and the overall pressure within the flask is 0. 1 atm. How many moles of co2 are in the flask? at this temperature, you may take the kh value for co2 as 0. 033 m / atm.

1 Answer

  • In this exercise we want to calculate the amount of moles, so this is going to be:

    [tex](4.6)(10^{-3}) \ mols \ CO_2[/tex]

    Knowing that Henry's law is given by:

    [tex]C = KHP[/tex]

    Where constants are given by:

    • C = Concentration  
    • KH = Henry's law constant = [tex]0.033 m/atm[/tex]
    • P = partial pressure = [tex]0.07 atm[/tex]

    Before we can find the concentration of CO2 (and hence the moles of CO2), we first need to find its partial pressure.  We look up the vapor pressure of water at 25º and find it to be 0.03 atm.  Since the total pressure is equal to 0.1 atm, this mean the partial pressure of:


    [tex]CO_2 = 0.1 \ atm - 0.03 \ atm = 0.07 \ atm[/tex]

    Now using Henry's law, we find the concentration:

    [tex]C = (0.033)*( 0.07) = (2.31)*(10^{-3})[/tex]

    Converting to moles of CO2, we have:

    [tex](2.31)*(10^{-3})*( 2) = (4.6)*(10^{-3})[/tex]

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