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Describe how the surface charge characteristics of hydrous oxides and 2:1 layered phyllosilicates differ

Describe how the surface charge characteristics of hydrous oxides and 2:1 layered phyllosilicates differ

Soil and Water Chemistry Midterm Exam (due by the end of 3/8/19)

Please provide concise but complete answers, using your knowledge of soil and water chemistry. Pay attention to the points given to each question when dividing your effort. Use any source but work individually. Cite any important source you used if it was not the text or the lecture notes.

1. Briefly describe the structural differences between hematite and goethite. Why does climate affect the relative amounts of these two minerals in soils? (5 pts)

2. Describe how the surface charge characteristics of hydrous oxides and 2:1 layered phyllosilicates differ. (5 pts)

3. Exactly why would kaolinite make a better sorbent for nonpolar organic molecules than smectite or vermiculite? (5 pts)

4. Why is it difficult to accurately determine weathering rates in soils? (5 pts)

5. Describe the general weathering scheme of muscovite to dioctahedral vermiculite. (5 pts)

6. Calculate the activities coefficients for Al3+ and K+ in a soil solution in which they are each 1 mmolar (10-3 molar) and the balancing anion is SO4-2. Show your work. Why are they so different? (5 pts)

7. Phosphorus is not a macronutrient and there should be plenty of total P in most soils. Why is often necessary to add more P to obtain optimum plant growth? (5 pts)

8. You’ve had a garden for a number of years and have added dairy manure compost to provide nitrogen. Now your soil test is ‘excessive’ in phosphorus. Is this a problem for your garden plants; for your local water body; for your self esteem? What should you do about it? What form of phosphorus is your soil test measuring? (10 pts)

9. What is the basis for your group project, i.e. why is this research being done? How will your results be useful? (10 pts)

10. In your own words, explain the new ‘model’ for the molecular structure of soil organic matter (e.g. as detailed in Lehmann and Kleber, 2015—available on Blackboard under readings). What types of bonding keeps it together? Does this model make more sense than the older humic/fulvic acid model? Which model do you believe is correct and why? (15 pts)

11. As an expert, you have been asked to testify on the benefits of soil organic matter before a House subcommittee. Summarize the main points you would make and how you would support them with soil chemistry (i.e. what we’ve learned in this course). (15 pts)

12. As an expert, you have been asked to explain how soils can be used to sequester carbon and help ameliorate climate change. You audience is an intro soils course. Summarize your main points and discuss the different ways that carbon can be stabilized. Include a discussion of your views on soil organic matter recalcitrance. (15 pts)

13. Extra credit. You need to prepare a synthetic ‘acid rain’ solution that is equal molarity sulfate and nitrate. You have solutions of 1.00 molar HNO3 and 1.00 molar H2SO4. How many mLs of each would you dilute to 1 liter to create a pH 4.0 solution? Show your work. (5 pts)

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