1.   Discuss some of the reasons for the observed cation exchange phenomena in soils.

2.   What are the origins and relative magnitudes of the negative charges of the soil inorganic fraction?

3.   Under what circumstances might a soil be expected to take on a net positive charge?

4.   Why do certain clay minerals expand in water while others do not?  Give examples.

5.   What  is the so-called pH-dependent cation exchange capacity and what causes it?

6.   What is meant by the terms 1:1 and 2:1 minerals?

7.   To  what  extent do the expandibility and particle  size  of clay minerals affect the CEC?

8.   Soil A is found to have a cation exchange capacity of 40 cmol kg-1. Soil B has a CEC of 15 cmol kg-1.
9.   In a table headed as follows:
             Colloid         Lattice                               source                Approximate
              name            type          Expandability         of charge              CEC (cmol kg-1)
     List at least four common soil constituents and give their properties.  
     Discuss how the various properties affect measured CEC.

10.  What is an Isoelectric Point?  From whence does it arise (in soils)?  What role does it play in soils?  

11.  List four common soil colloidal constituents and discuss their respective impact upon soil chemistry.

12.  What is the difference between a dioctahedral and a trioctahedral mineral?  Give some examples of each.

13.  What is the difference between hydrolysis and hydration?  Give examples of each.

14.  Explain the concept of weathering. What occurs during this process? Why are some minerals more resistant to

     weathering than others? How can this be related to soil formation?
15.  How might one predict the process of weathering and secondary mineral formation without making many measurements
     over a long period of time?
16.  What is soil organic matter? Why is it important to know something about this material? What components of the soil
     organic matter are most important in soil chemistry?
17.  Why is concentration insufficient for studying soil chemical reactions?  What is used instead? 

18. Explain complexation. What is the difference between inner sphere and outer sphere complexation? 

19.  What is an equilibrium constant? How do solubility products, complexation products, acid dissociation  products,

     etc. differ?
20.     Be able to define the terms used in class.
21.  Three processes were listed as being of primary importance in weathering of minerals, these being:
       Explain and give examples of how each will be a factor in weathering of minerals in the soil. 

22.  When discussing weathering, the formation of secondary minerals in soils formed from igneous rock 
     was shown to be a function of average annual rainfall. Explain why this should occur.

23. The cation exchange capactiy of Mica, which has a very high unit crystal charge, can be only about twice that
    of kaolinite, which has no unit crystal charge, whereas the cation exchange capacity of smectite, with an
    intermediate unit crystal charge, can be 10 times higher than that of kaolinite. Explain this phenomonon.
24. Why are we constantly relating mineral solubility to pH?

25. Solubility of minerals can be plotted as activity diagrams, and would describe a line on a two dimentional

    plot and a plane on a three dimentional plot. If the solution is in equilibrium with the solid phase activity
    of the plotted components must fall on the line or plane. How does one interpret data which falls above or below
    the line/plane? If two different minerals are plotted in the diagram what kind of interpretations can be made if
    the two line/planes are different and parallel? If they cross somewhere in the plot?
26. Aluminum is considered to be an acid component of the soil. Why should this be true? 


1. Discuss some of the reasons for the observed cation exchange phenomena in soils. 

2. Draw a diagram for a "typical" soil titration curve. Explain why such a curve is obtained.

3. You would like to cause a dispersed colloidal suspension to flocculate. How would you proceed? What is the
   theoretical basis of your method (ie. why does it work?). Hint: colloids usually remain suspended as a result of
   coulombic repulsion. 

4. What kind of problems may arise in measuring the pH of colloidal systems. 

5. Indicate a few factors that can influence a measured CEC and explain the influence. 

6. Statement: For best plant growth, one should always be sure the pH is between 6.5 and  7.0.  Comment. 

7. Explain how variations in the thickness of the double layer might affect plant nutrition. 

8. Explain the ion-selectivity concept and indicate its importance in soil chemistry and plant nutrition.

9. Discuss the importance of the "suspension effect" in soil chemical problems.

10. Some years ago the "Shultz-Hardy rule" was formulated. Basically, this says that as valence of the saturating cation

    is increased, clays become progressively better flocculated. How might this phenomenon affect soil chemical
    properties? Plant nutrition? 

11. Explain the difference between the Helmholtz, Gouy, and Stern theories of the clay surface. Indicate how

    these theories might lead to different interpretations of soil chemical relationships. 

12. What soil properties and/or constituents determine it's  buffering capacity?  Explain how the properties
13. What is the complimentary ion effect? How does understanding this phenomenon assist our understanding

    of plant nutrition?

14. Assume you are addressing a group of farmers and business persons who are not so conversant with the technical
    aspects of plant nutrition, soil fertility and nutrient pollution problems. Your missionis to explain to this
    group the nature of cation exchange and why it is important. How would you proceed? 

15. Assuming the Stern model of the electric double layer is correct, explain (with help of diagrams) how the double

    layer thickness and zeta potential might change with increasing electrolyte concentration and increasing valence
    of counterions. 

16. Given: A "typical soil profile might have pH values approximating the following:

          Horizon          Depth from surface (in.)          pH
             1                      0-2                     3.6
             2                      2-3                     3.8
             3                      3-5                     4.1
             4                      5-11                    4.9
             5                     11-22                    5.0
             6                     22-32                    5.1
             7                     32-45                    5.1
    From your knowledge of aluminum chemistry in aqueous systems, in which horizon(s) would you expect to
    find the most Al? The least Al? Why?
17. If you search the literature, you will find that soil pH is reported to the nearest tenth about half the time and to
    the nearest hundredth the other half. In fact it is not impossible to occasionally find soil pH reported to the
    nearest one thousandth of a pH unit. Comment on the appropriateness of such presentations.
18. Soil pH is highly important in the proper growth of many plants, so soil scientists have expended considerable
    research effort on understanding soil reaction and the amount of lime required to establish an optimum pH. Discuss
    the "optimum pH" concept, and some the soil factors influencing pH and lime requirement.
19. Describe the Quantity/Intensity approach to soil testing. What are the advantages and/or disadvantages of this
    approach as compared to other methods we have discussed?
20.  How and why does Al enter the soil acidity picture?
21. An acidic pesticide of pK 5.0 is being applied to soils of a given region. Would leaching be greatest for soils of
         a) pH > 5,
         b) pH 6 to 8, or
         c)  pH < 5?
    Justify your answer. 

22. What is the difference between specific and non-specific adsorption in soils?

23. One of the introductory comments for this course was that soil is both a sink and source for ions. On the
    basis of what you have learned so for, give reasons for such a statement.  Using a specific ion, discuss the
    various reactions which will occur as the soil becomes either a sink or a source. 

24. Let us assume that we could find four soils formed under identical circumstances, except that the soil

    forming processes had been progressing for 103, 104, 105, and 106 years.  Let us further assume that the parent
    materials of all four soils are mica-rich granites. How would you expect these soils to differ chemically and
25. If the above soils had never been fertilized, what differences might they exhibit in ability to supply nutrients
    to plants?
26. A practice finding increasing favor is the use of soils as a terteriary treatment system for sewage effluent.
    Phosphorus is of particular interest in this regard, since it has been cited as a causative factor in surface
    water eutrophication.  What soil properties should one consider in determining how effective a soil would be
    in removal of phosphorus, and why?
27. Now, consider the welfare of plants rather than water quality. What are some of the factors one needs to consider
    in applying the waste water to soils, and why? Remember, the effluent will contain a wide variety of inorganic
    substances, the exact contents being dependent upon the domestic/ industrial mix of wastes being treated.
28. During the summer months, deep lakes tend to form a thermal stratification with a very sharp boundary between
    warm water above and cold water below.  It has been found that gasses do not readily diffuse from one temperature
    zone to another, so the lower layer is normally depleted in oxygen. Let us assume the lake is well along its way in
    the eutrophication process, so there is a plentiful amount of organic matter in the bottom sediments to serve as
    a microbial energy source. Discuss the type of chemical reactions which will occur in the "soil" at the lake bottom
    and the resultant effect on overlying water quality. 

29. A particular soil may contain up to 3% K, yet plants growing on the soil might show good response to potassium

    fertilization.  However, the same plant species growing on a soil containing less K might show less response to K
    fertilization. Explain, including in your discussion a discussion of why various soils differ in their ability to
    provide K for plant needs. 

30. Mr. Smith always had a nice looking front lawn. However, one evening he noticed that his neighbor, Mr. Jones'

    front lawn was several shades greener than his own. This would never do! The next morning, he proceeded forthwith
    to the local Agway store and bought two bags of urea (anyone knows that a green lawn requires plenty of N), which
    he immediately spread on the lawn. He couldn't help gloating a bit as his lawn, within a week, became considerably
    greener than Mr. Jones'. However, to his horror, the dark green slowly changed to maroon, indicating P deficiency.
    In terms of reactions occurring in the soil, explain what happened. What would you recommend be done to correct the
    situation? What plant nutrients other than P might have been affected?

31. You have probably seen dead trees in the middle of Beaver ponds, drowned corn in low, wet spots, etc. In fact, most

    plants are quite unhappy with wet feet. In terms of soil chemical reactions, what might cause plants to die when the
    soil becomes waterlogged?
32. During the semester, we have periodically discussed and mentioned ion selectivity as it relates to chemical reactions
    in soils and plant nutrition.  What is ion selectivity? Give a few situations in which selectivity might be important
    and explain the importance in terms of soil reactions. 

33. The mineral fraction of highly weathered soils such as those found in Southern United States and in tropical regions

    is primarily made up of kaolinite and sesquioxides. What effect does this have on plant nutrient supplies?
    Explain the effects. 

34. Discuss the soil reactions and relationships that would likely result from liming an acid soil (say pH 4.5) to

    pH 7.0 and maintaining the pH at the higher level. 

35. Discuss the chemistry of iron and aluminum and explain their importance in soil chemical equilibria.

36. Explain how the five soil forming factors (time, temperature, parent material, vegetation, and topography) might

    affect the chemical characteristics of soils. 

37. A modern fertilizer might typically contain such materials as KCl, (NH4)2 HPO4, and Ca(H2PO4)2. Postulate the

    fate of these materials when added to a soil at pH 6.5. 

38. Discuss the weathering of mica as it pertains to reactions in the soil. 

39.  Why is Al considered a soil acid?

40. What type of soil factors are involved in adsorption of organic "pollutants" such as pesticides? 

41. In temperate region soils, the amount of buffering tends to be proportional to the aluminum content of a soil.


42. The potassium cycle in soil is relatively simple, and can be roughly divided into three categories:

          1) exchangeable K, which is on the exchange complex, and available to plants;
          2) K occurring as a part of the mineral structure, and completely unavailable to plants;
          3) a "fixed" fraction which is not really considered as "mineral K", but is not readily available
             to plants either.

    Discuss the factors that influence the relative amounts of K in each of these fractions and why the K is thus affected. 

43. There is evidence that phosphorus adsorption by soils is related primarily to organic matter and aluminum in the

    soil. Discuss the types of reactions that might be occurring and the implications to availability of phosphorus
    fertilizer added to the soil. 

44. Although the major emphasis of this course has been on inorganic reactions occurring in the soil, the impact of the

    organic fraction has frequently been mentioned. Discuss the extent to which availability of the three major plant
    nutrients, N, P, & K, are affected by soil organic mater. Include a discussion of the reactions that will be
    involved (as appropriate). 

45. It has been shown that soils exhibit ion selectivity. How might this affect availability of K to plants? What

    effect will soil pH likely have on the indicated relationship Why? 

46. Along with aluminum, iron has frequently been mentioned as an important element in soil chemical reactions. In what

    types of reactions is this element important and how is its influence "felt"? 

47. Nitrogen, phosphorus, several heavy metals and trace elements, and various organics such as pesticides or

    hydrocarbons can become potential soil problems.  Restricting yourself to N and heavy metals what are the potential
    problems involved in using soils for disposal of materials containing these pollutants?  Why would it likely be
    a problem? 

48. To a pH 5.0 solution in equilibrium with solid phase variscite (A1P04@2H20) one adds calcium carbonate (CaC03).

    Qualitatively, discuss predicted changes that will occur in the system, including equilibrium reactions where

49. For a variety of reasons, no-till agriculture is becoming popular in eastern U.S. Discuss the soil chemical changes

    that might occur when "conventional" tillage practices (i.e. turning over the surface 6-8 inches and tilling
    to a satisfactory seedbed) are replaced by "no-till" practices (i.e., only a strip wide enough to plant the seed
    is disturbed. Growing vegetation is usually killed with herbicides). Also, discuss any needed changes in fertilizer

50. What are the common electron acceptors for soil? Under what conditions does each become important? What effect

    would these conditions have on plants and microbes? 

51. As ocean dumping of wastes has been curtailed by EPA, increasing pressure for land disposal has been exerted.

    This is no real problem if the waste is a sludge from a waste-water treatment plant serving an entirely domestic
    community, since the sludge is not likely to be very different from animal manure. However, if the plant serves
    an industrial community, a high probability exists that the sludge contains potentially toxic heavy metals. What
    are the potential problems involved in using soils for disposal of sludges containing heavy metals? How would soil
    chemistry be involved with the problem and with solutions? 

52. What reactions are responsible for retention/fixation of phosphorous in acid soils? Basic soils? 

53. Indicate the sequence of events that occur upon exclusion of gaseous oxygen from a soil by waterlogging.

    What will be the approximate E7 for each event? How (and why) would you expect biological systems to be affected
    by this sequence of events? 

54. Explain why measurement of total soil analysis practiced in the early 1900's proved to be a poor indicator of the

    amounts of ions which may enter the food chain. 

55. Farmers report that when they shift cultural practices from the reliance upon "Manufactured" fertilizers and

    pesticides which has developed since WW II to the more traditional "organic" methods of crop rotations, proper
    additions of organic wastes (e.g. distribution of manure at 2-3 tons per acre rather than disposal of manure at up
    to 40-50 tons per acre), use of "rock flours' as fertilizers, etc., they experience a near-catastrophic drop in crop
    yields the first year, followed by a slow recovery. After about 3 or 4 years the yields are nearly back to
    "pre-organic" levels, where they tend to stabilize. If you read Rodale Press and other similar publications, you
    know this phenomenon is attributed to a "poisoning" of the soil. However, much of the effect can be predicted and
    explained on the basis of the soil chemistry.  Please do so. 

56. Jackson has called aluminum reactions the "unifying principal in soil science". If this is true, then all soil

    reactions should, in some way be related to aluminum chemistry. Recognizing that many soil reactions are similar
    to those of either P or K, explain how aluminum reactions will affect plant availability of these two nutrients.

57. A farmer/gardener alters his cultural practices to incorporate more organic matter into the soil. List some of the

    effects this may have on inorganic reactions within the soil and/or availability of nutrients to plants. In each
    case, briefly indicate why or how the effect occurs. 

58. Describe the sequence of events (chemically) that occurs when a soil becomes anaerobic. How does this affect

    availability of nutrients to plants? Recognizing that lake or ocean sediments are "soils under water" and streams
    frequently originate in marshes, how would this affect water quality? 

59. Most soils contain far more potassium than is available at any one time.  What are the processes causing the

    unavailable potassium to become available?  Under what circumstances might the potassium revert to a less available

60. On the basis of equilibrium chemistry, discuss the soil solution changes that might be expected to occur when a

    soluble form of phosphorus is added to the soil as fertilizer. 

61. Discuss the soils' role in cycling K in the food chain. 

62. Over recent years there has been an increasing concern about the impact of so-called "acid precipitation" on the

    environment. Because managed ecosystems (eg. farms) include practices which counteract soil effects, impact on soil
    is usually restricted to natural ecosystems. Acid precipitation will usually consist of weak solutions (10-3 to 10-5)
    of sulfuric and/or nitric acid. From your knowledge of soil chemistry, how would you expect soil to be affected? What
    type of soil would you expect to be most sensitive? 

63. Due to copper's tendency toward passivation, most medieval churches were roofed with copper, and green roofs have

    long been a dominant feature of the landscape in Europe. After withstanding weather for hundreds of years, many of
    these roofs are beginning to leak, as are copper roofs installed since World War II. What has happened?  How might
    this observation be related to metal reactions in soils?
64. Soil pollution is becoming an increasing concern to soil scientists. Modern society not only sees land as a valid
    place to discard wastes such as municipal sludge, but normal societal activities from food production to lawn care
    continually add chemicals to the soil. Even beneficial chemicals such as fertilizer can be a pollutant when added in
    excessive quantities. Using a heavy metal such as Cu as an example, explain how and why this plant nutrient can be a
    pollutant. For any given amount of Cu input, what soil properties or characteristics will most likely decrease the
    chance of pollution occurring?
65. You decide that it is time to improve your lawn, so you send a soil sample to the state lab for testing (the usual
    test is for exch. K, which is assumed to be a measure of that available). The return indicates that the  soil K level
    is very low and you need to add some of this element to your lawn.  Being a college graduate, you decide to do things
    scientifically, so you set up an experiment in which 0X, 1/2X, 1X, and 2X the amount of K recommended is added.
    Amazingly, you get no response to the added fertilizer.  You discuss this with a family member in another town, and
    she reports just the opposite: the soil test indicated adequate amounts of K in the soil, but the lawn always
    responded to K fertilization.  Explain the discrepancy.