1. Soil Solution

2. Calculating Activity Coefficients
Debye-Hueckel Limiting Equation:
log g = Z2 I1/2 for I < 0.01
Extended Debye-Hueckel Equation:
  for I < 0.1
Davies Equation:
for I < 0.5
B is a temperature dependent constant 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) H2O <--> Fe(OH) H+ K =  
Fe(OH) H2O <--> Fe(OH)3o + H+ K =  
Fe(OH)3o + H2O <--> Fe(OH) H+ K =

9. Hydrolysis Reactions: Anionic
log K
H3PO4o  H+ + H2PO  
H2PO4-  H+ + HPO  
HPO42-  H+ + PO

10. Complex Equilibria

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

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

14. Dissociation Reactions
Log K
H2CO3  H+ + HCO
HCO3-  H+ + CO  
CaCO3 (s)  Ca CO

15. Equilibrium Equations
Log K
H2CO3  H+ + HCO
HCO3-  H+ + CO
H2O  H+ + OH
CaCO3 (s)  Ca CO
CO2(aq) = KH PCO2  

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

17. Species Distribution
H2CO3
HCO3-
CO32-

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