E-chem Exam

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E-chem Exam
2013-10-10 13:24:54

Solubility, smog, ph
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  1. Equilibrium Constant expression

  2. 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
  3. 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.
  4. 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
  5. Solving ph for a buffer
    • HA + H2O = H3O+ + A-  

    • Na+ + A- + H2O=OH- + HA + Na+          
  6. Ka
  7. Kb
  8. 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.
  9. Alkalinity
    comes from charge balance.  

    # negatively charged species = # positively charged species
  10. 4 major groups of clay
    • Kolinite
    • illite
    • chlorite
    • montmorillonite
  11. Kaolinite
    product of intense tropical and desert weathering. Most found in equatorial sediments. Note lack of exchangeable cations…
  12. Chlorite
    • polar sources
    • physical weathering 
    • lots of exchangeable ions
  13. 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)
  14. Montmorillonite
    • expanding clay
    • weathering in poor drainage areas
    • in situ weathering product of volcanic ash
  15. Soap
    potassium or sodium salt of a fatty acid
  16. detergent
    acts to reduce interfacial or surface tension
  17. Partial Pressure
  18. Biological pump of carbon
    life such as plants that use photosynthesis to creat organic carbons form the atmosphere
  19. Physical ocean pump
    oceans take up 2.2Gt/yr of carbon due to solubiliy
  20. Solubility Product
    Ksp=[X]a[Y]b= XY in molarity
  21. Why organic matter is important
    –Building blocks for life/energy source for heterotrophs

    –Global C cycle

    –O2 balance


    • –Affects
    • contaminant transport

    • –Affects
    • nutrient transport

    • –Affects
    • light penetration
  22. DOM
    Dissolved organic matter
  23. POM
    Particulate organic matter
  24. Humic Matter
    -leftovers of biologically-produced material


    -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
  25. Humic Acid
    • soluble in alkaline solutions, insoluble
    • below pH 1 (I have also seen pH 2 used as criterion)
  26. Fluvic Acid
    • alkaline extractable, soluble over whole
    • pH range
  27. Humin
    Insoluble in acid or base
  28. Humic substance charatceristics
    • - have aromatic character, phenolic OH
    • groups, carboxylic groups, aliphatic OH groups
    • -yellow or brown color
  29. why [H+]2
    H+=Aas long as the dissosciation of HA is the main source of H+ ion and not water
  30. Kw=KaKb=10-14
  31. [HCO3]=