ANALYTICAL CHEMISTRY Chem 333

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ANALYTICAL CHEMISTRYChem 333
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Chapter 9Systematic Treatment of Equilibrium
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Equilibrium Systems Can be Complex
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Effect of Increased Atmospheric CO2 Levels
Increased PCO2 levels cause a decrease in the pH
of the ocean.
Dissolved CO2
Carbonic Acid
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Geochemical Consequences of Increased Atmospheric
Carbon Dioxide on Coral Reefs
Dissolution of coral reefs
Important reaction to consider
Coral reefs are composed of calcium carbonate
What does Le Chateliers predict will happen to
the coral reefs as the result of reduced oceanic
pH?
They are likely to dissolve!
Kleypas, J. A. et al Science 1999, 284, 118-120.
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Geochemical Consequences . . .
Calcium carbonate saturation state (W)
Decreased pH decreases W
Kleypas, J. A. et al Science 1999, 284, 118-120.
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Geochemical Consequences . . .
Calcium carbonate saturation state (W)
Kleypas, J. A. et al Science 1999, 284, 118-120.
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Reef Calcification Rates
Reef building requires that organisms deposit
CaCO3 in excess of physical, biological, and
chemical erosion.
A 10 to 20 decrease in CaCO3 production will
pose a significant deficit in many coral reefs.
Kleypas, J. A. et al Science 1999, 284, 118-120.
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List of Some of the Important Reactions to
Consider
Kw 1.00 x 10-14
Ks 0.0344
KC 1.30 x 10-3
Ka1 2.00 x 10-4
Ka2 4.69 x 10-11
Ksp 2.00 x 10-8
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Systematic Treatment of Equilibrium
1) Write pertinent reactions
2) Write the charge balance equation
3) Write mass balance equation(s)
4) Write the equilibrium constant for each
reaction
5) Count equations and unknowns
6) Solve
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Charge Balance
Solutions must have zero charge!
z charge of ion
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Charge Balance
Charge Balance
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-3
Cation 3Anion
Cation
Anion

Total Charge 3
Total Charge -3
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Mass Balance
Simply put statement of the conservation of
mass or matter
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Magnesium Hydroxide
Calculate the concentration of each ion in a
solution of 4.0 x 10-8 M Mg(OH)2 that is
completely dissociated into Mg2 and OH-.
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LaF3
Calculate the solubility of LaF3 dissolved in a
buffer of pH 3.