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Compare the Ks0 values of MnCO3(s)

  1. Oct 12, 2014 #1
    1. The problem statement, all variables and given/known data
    compare the Ks0 values of MnCO3(s) in fresh water (I=0) and in estuarine waters (I=0.08) at 25°C. If each of the waters contained a concentration of CO32- equal to 10-6M and MnCO3(s) controls the Mn solubility, what is the Mn2+ concentration in each water? What is the Mn2+ activity in each water?

    2. Relevant equations
    MnCO3 (s) = Mn2+ (aq) + CO32- (aq)

    Ks0 = {Mn2+}{CO32-} / {MnCO3 (s)}

    Ks0 = yMn2+[Mn2+] yCO32-[CO32-]

    3. The attempt at a solution
    Not sure how to start. Any suggestions are greatly appreciated!
     
  2. jcsd
  3. Oct 12, 2014 #2
    Maybe I'm just not understanding what the problem means. Does it mean if [CO32-] is 10-6M and the ratio of CO32- to Mn2+ is 1:1 in the chemical equation then [Mn2+] is also 10-6M? Is this how others are interpreting the problem?
     
  4. Oct 12, 2014 #3

    Borek

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    Staff: Mentor

    Calculate concentration of Mn2+ assuming solution is saturated AND concentration of CO32- is 10-6.
     
  5. Oct 12, 2014 #4
    Then an ICE table should be used? Something like this?



    ____________MnCO3 (s)__________Mn2+ (aq)________CO32- (aq)

    Initial___________solid______________0_______________10-6M

    Change__________-x_______________+x__________________+x

    Equilibrium______-x_______________+x______________10-6M + x
     
  6. Oct 13, 2014 #5

    Borek

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    Staff: Mentor

    No, no need for ICE table.

    Write formula for Ksp. You know Ksp value, you know concentration of CO32-, the only unknown is the concentration of Mn2+. And solving for the concentration of Mn2+ is trivial.
     
  7. Oct 13, 2014 #6
    Ksp = [Mn2+][CO32-]
    Ksp = [x][x]
    x= 10-6M
    Ksp = (10^-6M)(10^-6M)
    Ksp = 1.0x10^-12

    Is this right?
     
  8. Oct 13, 2014 #7

    Borek

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    Staff: Mentor

    No, you are doing strange things. That means you are completely confused about something.

    First - find Ksp value in the Ksp tables. What is the value?
     
  9. Oct 13, 2014 #8
    Ohh I see what you're saying not, Ksp is 2.2 x 10-11.
     
  10. Oct 13, 2014 #9

    Borek

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    Staff: Mentor

    Now plug the Ksp and CO32- concentration into Ksp formula, and solve for the only unknown.
     
  11. Oct 13, 2014 #10
    Gotcha, that's simple! I was over thinking it. Thank you oh mighty chemistry guy. So in my above equation Ks0 = yMn2+[Mn2+] yCO32-[CO32-], can Ksp be put in for Ks0?

    2.2x10^-11 = [Mn2+] (10^-6M)
    2.2x10^-5 = [Mn2+]
     
    Last edited: Oct 13, 2014
  12. Oct 14, 2014 #11

    Borek

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    As far as I can tell Ksp and Kso are different symbols used for exactly the same constant.

    Just in case someone wonder what your equation means. I guess it is

    [tex]K_{sp} = \gamma_{Mn^{2+}}[Mn^{2+}]\gamma_{CO_3^{2-}}[CO_3^{2-}][/tex]
     
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