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Soil Solution

Soil Solution. Davies Equation : for I < 0.5. Debye-Hueckel Limiting Equation : log g = - 0.511 Z2 I 1/2 for I < 0.01 Extended Debye-Hueckel Equation: for I < 0.1. Calculating Activity Coefficients. B is a temperature dependent constant (0.33 @ 25 °C)

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Soil Solution

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  1. Soil Solution

  2. Davies Equation: for I < 0.5 Debye-Hueckel Limiting Equation: log g = - 0.511 Z2 I1/2 for I < 0.01 Extended Debye-Hueckel Equation: for I < 0.1 Calculating Activity Coefficients B is a temperature dependent constant (0.33 @ 25 °C) a is an effective ion size parameter

  3. Ions in Solution: Coordination by Water Molecules

  4. Ions Pairs (Outer-sphere)

  5. Ions Complex (Inner-sphere)

  6. Reaction Driving Force

  7. Hydrolysis Reactions Fe3+ • 6H2O Fe(OH)2+ • 5H2O

  8. Hydrolysis Reactions Fe3+ + H2O <--> Fe(OH)2+ + H+ K = 10-2.19   Fe(OH)2+ + H2O <--> Fe(OH)2+ + H+ K = 10-3.5 Fe(OH)2+ + H2O <--> Fe(OH)3o + H+ K = 10-7.4 Fe(OH)3o + H2O <--> Fe(OH)4- + H+ K = 10-8.5

  9. Hydrolysis Reactions: Anionic log K H3PO4o H+ + H2PO4- -2.15  H2PO4- H+ + HPO42- -7.20  HPO42- H+ + PO43- -12.35

  10. Complex Equilibria

  11. Carbonate Species/Reactions H2O CO2 (g)  CO2(aq)   H2CO3 CO2(aq) + H2O H2CO3 H+ + HCO3- HCO3- H+ + CO32- CaCO3 (s)  Ca2+ + CO32-

  12. CO2 Hydration H2O CO2 (g)  CO2(aq) CO2(aq) = KH PCO2 KH = Henry's Law Constant = 0.033 M (at 25 °C)

  13. Dissociation Reactions Log K H2CO3 H+ + HCO3- -6.36 HCO3- H+ + CO32- -10.33   CaCO3 (s)  Ca2+ + CO32- -8.35

  14. Equilibrium Equations Log K H2CO3 H+ + HCO3- -6.36 HCO3- H+ + CO32- -10.33 H2O  H+ + OH- -14 CaCO3 (s)  Ca2+ + CO32- -8.35 CO2(aq) = KH PCO2

  15. Mass and Charge Balance mass [C]T = [H2CO3*] + [HCO3-] + [CO32-] + [CaCO3] [H+] + 2[Ca2+] = [OH-] + [HCO3-] + 2[CO32-] charge

  16. Species Distribution H2CO3 HCO3- CO32-

  17. Simplifying Assumptions (!) 1. At pH < 9, [CO32-] << [HCO3-], [H2CO3*] 2. At PCO2 > 10-3.5 atm, [HCO3-] >> [OH-] [HCO3-], pH 7 = 1.44 mM mass [C]T = [H2CO3*] + [HCO3-] + [CaCO3] [H+] + 2[Ca2+] = [HCO3-] charge

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