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Equilibrium Constant expression
aW+bX->cY+dZ
K=[Y]c[Z]d/[W]a[X]b
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Types of equations for solving multiple Equilibria
- Equilibrium-constant equations
- Mass-balance equations
- –Relate
- equilibrium concentrations of species with the analytical concentration of
- solutes
- Charge-balance equations
- –Based
- on idea that electrolyte solutions have to be electrically neutral
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Charge balance equations
- # moles positive charge/L = # mols negative charge/L
- Remember that the # mol gets multiplied by charge to give the moles of charge, e.g., for 0.20 mol Mg2+, there are 0.40 mol of positive charge.
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Steps for solving mutiple equilibria
- 1)Write balanced chemical equations for all
- relevant equilibria
- 2)State in terms of equilibrium conc. the
- variable being sought
- 3)Write equilibrium constant expressions
- for all the equilibria and find the appropriate K values
- 4)Write mass balance expressions
- 5)Write any available charge-balance
- expressions
- 6)Make sure # of unknowns equals # of
- equations. If not, try to approximate
- concentrations of some of the unknowns
- 7)Approximate as possible to simplify the algebra
- 8)Solve the equations
- 9)Check validity of approximations
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Solving ph for a buffer
- Na+ + A- + H2O=OH- + HA + Na+
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Assumptions for buffers
- 1.if Ka or Kb
- is >10-3 (strong acid or base)
- 2. if the molar concentrations of HA or A- are very small so that the assumptions
- that we can ignore [OH-]
- and/or [H3O+]
- no longer hold.
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Alkalinity
comes from charge balance.
# negatively charged species = # positively charged species
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4 major groups of clay
- Kolinite
- illite
- chlorite
- montmorillonite
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Kaolinite
product of intense tropical and desert weathering. Most found in equatorial sediments. Note lack of exchangeable cations…
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Chlorite
- polar sources
- physical weathering
- lots of exchangeable ions
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Illite
- one of the most common clays.
- High in potassium
- Land-derived, in oceans highest in concentration in midlatitudes in the northern hemisphere (which has more land)
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Montmorillonite
- expanding clay
- weathering in poor drainage areas
- in situ weathering product of volcanic ash
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Soap
potassium or sodium salt of a fatty acid
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detergent
acts to reduce interfacial or surface tension
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Partial Pressure
X=PCO2/Ptotal
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Biological pump of carbon
life such as plants that use photosynthesis to creat organic carbons form the atmosphere
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Physical ocean pump
oceans take up 2.2Gt/yr of carbon due to solubiliy
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Solubility Product
Ksp=[X]a[Y]b= XY in molarity
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Why organic matter is important
–Building blocks for life/energy source for heterotrophs
–Global C cycle
–O2 balance
–Climate
- –Affects
- contaminant transport
- –Affects
- nutrient transport
- –Affects
- light penetration
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DOM
Dissolved organic matter
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POM
Particulate organic matter
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Humic Matter
-leftovers of biologically-produced material
-Heterogeneous
-Biologically refractory
-Involved in photochemical reactions
-Form complexes with metals
-Involved in hydrophobic interactions with anthropogenic organic compounds
-Form disinfection by-products during drinking water treatment
-Affect soil fertility, also weathering processes
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Humic Acid
- soluble in alkaline solutions, insoluble
- below pH 1 (I have also seen pH 2 used as criterion)
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Fluvic Acid
- alkaline extractable, soluble over whole
- pH range
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Humin
Insoluble in acid or base
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Humic substance charatceristics
- - have aromatic character, phenolic OH
- groups, carboxylic groups, aliphatic OH groups
- -yellow or brown color
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why [H+]2
H+=A- as long as the dissosciation of HA is the main source of H+ ion and not water
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Kw=KaKb=10-14
Kw=[H+][OH-]
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