Speciation Plus more species  gases and minerals!!

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Aqueous Complexes Why do we care??

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Presentation transcript:

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)2 CaF+ CaOH+ Ca(O-phth) CaH2SiO4 CaPO4- CaB(OH)4+ CaH3SiO4+ CaSO4 CaCH3COO+ CaHCO3+ CaHPO40 CaCO30 Plus more species  gases and minerals!!

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??

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

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

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

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.