1. Speciation Plus more species  gases and minerals!!
Any element exists in a solution, solid, or gas as 1 to n ions, molecules, or solids
Example: Ca2+ can exist in solution as:
Ca CaCl CaNO3+
Ca(H3SiO4) CaF CaOH+
Ca(O-phth) CaH2SiO CaPO4-
CaB(OH) CaH3SiO CaSO4
CaCH3COO CaHCO CaHPO40
CaCO30
Plus more species  gases and minerals!!

2. How do we know about all those species??
Based on complexation  how any ion interacts with another ion to form a molecule, or complex (many of these are still in solution)
Yet we do not measure how much CaNO3+, CaF+, or CaPO4- there is in a particular water sample
We measure Ca2+  But is that Ca2+ really how the Ca exists in a water??

3. Aqueous Complexes Why do we care??
Complexation of an ion also occurring in a mineral increases solubility
Some elements occur as complexes more commonly than as free ions
Adsorption of elements greatly determined by the complex it resides in
Toxicity/ bioavailability of elements depends on the complexation

4. Defining Complexes Use equilibrium expressions: cC + lHL  CL + lH+
Where B is just like Keq!

5. Mass Action & Mass Balance
mCa2+=mCa2++MCaCl+ + mCaCl20 + CaCL3- + CaHCO3+ + CaCO30 + CaF+ + CaSO40 + CaHSO4+ + CaOH+ +…
Final equation to solve the problem sees the mass action for each complex substituted into the mass balance equation

6. Mineral dissolution/precipitation
To determine whether or not a water is saturated with an aluminosilicate such as K-feldspar, we could write a dissolution reaction such as:
KAlSi3O8 + 4H+ + 4H2O  K+ + Al3+ + 3H4SiO40
We could then determine the equilibrium constant:
from Gibbs free energies of formation. The IAP could then be determined from a water analysis, and the saturation index calculated.